Say what now?.
Let me explain...
The terms Universe and Setting, especially in Pop Culture and RPGs, are pretty much synonymous. They both denote the fictional milieu in which the stories being told are taking place.
That said, when I say 'Universes' I am thinking primarily of IPs, such as The Star Wars Universe, the DC Comics Universe, or The Ghostbusters Universe. These are massively popular franchises (to varying degrees of notoriety), generally familiar to anyone who is even remotely aware of Western/American pop culture.
I don't expect everyone at my gaming table to nod appreciatively or fist pump at the mention of my running a Five Star Stories game. On the other hand, I would very surprised if the majority of my players didn't get a little jolt of excitement should I suggest a Mass Effect or Game of Thrones campaign (Ha! Me? Run Middle Earth? Oh, I do entertain myself do I not?).
As evidenced by numerous posts before this one on everything from Alien to Pokemon to The Orville, I really enjoy running games in franchise universes. I find it strangely liberating. I can take the same amount of time I would devote to running a game in my own original setting and generate so much more material because a lot of the ground work has been done for me. I don't need to create a universe from scratch but rather add my own ideas to a universe many are already familiar with.
That familiarity is a key element as well. The buy in and suspension of disbelief required to make a Superhero or Space Opera game work is already there if the players come in knowing and liking the setting. It is easy to picture yourself on the bridge of a Starfleet vessel, inside the cockpit of an X-Wing Fighter, or battling a robot at the top of the Daily Planet building because you've seen those places many, many times. We know what they look like without having to really think about them.
As far as play materials and information go - character images, ship images, locations, handouts, information on key elements - IP universes are pure gold. A quick Google search of 'MiB Weapons' reveals dozens of descriptions and images of the Noisy Cricket, Series 4 De-Atomizer, Reverberating Carbonizer, and more. Can't wait for your favorite company to put out their new sourcebook on your franchise RPG, no worries! Wiki and the IP's fandom has your back.
For the purpose of what I am talking about here my personal view of what a 'Setting' is (as opposed to a Universe) is that the makers of the game you're running/playing created the world in which the game takes place so you can have an established world to game in.
In other words, instead of people liking Star Trek so much somebody said, "Hey let's make a Star Trek RPG", some one instead said, "We created this RPG. Hmmm. Now we need a Setting to go with it".
The biggest difference from this viewpoint is that in a licensed RPG, you know the Universe going in. In a RPG with an original setting, you learn about the setting for the first time when you read the game.
To be honest, I think it's very likely a great many modern RPGs have their setting and rules developed simultaneously. Unfortunately, for me at least, a lot of these Settings feel...what's the word I'm looking for? Lackluster? Cumbersome? Lackcumber?
More often than not, the original Settings that come with RPGs feel underdeveloped, overdeveloped, or just not particularly engaging to me. Take Mekton's 'Algol' Setting. It has everything you could want in a Giant Robot Anime world - An alien planet with exotic lifeforms, various governments and organizations doing battle in the field and courts of intrigue, and of course towering humanoid Mecha! It is also supremely boring. It's like they threw everything from every late 70s and early 80s Mech Anime in a mixing bowl and blended it until it had the flavor of mush - nothing distinctly stands out.
RIFTS is a game with a complex interweaving setting of everything, the kitchen sink, and it's mother and for the life of me I just can't easily picture it in my head. What does an average day look like on RIFTS Earth. Who do you see day after day on your way to and from work? Do people work like they do today? I've read through the main book a few times and I just can't get the feel of it beyond post-apocalyptic chaos. I hear that if I read through the correct dozen of it's multi-dozen splatbooks I'll get the hang of it. Yeeeah, no. That sounds excruciating.
I think part of it, perhaps a large part, is how I absorb the fluff of the milieu. With most IPs, I have slowly assimilated the Universe we're going to game in over the course of many years. As an example, by the time I first played the Star Wars RPG I had already lived with Star Wars for 10 years. I'd seen the movies all multiple times, collected the action figures and toys, read the comics, etc.
On the flipside, you hand me Runequest and tell me you'd love to play in Glorantha, the setting of Runequest created by the late, great Greg Stafford. OK, great. Assuming this is the first time I am seeing Runequest and Glorantha, I now have to absorb the look, feel, and particulars (important personalities, creatures, relevant history, governments, etc.) of this setting before we play. Can I? Well the real question is do I have the time to grasp what makes it awesome, what makes it tick, before we run our first session? Maybe, maybe not. It would depend very much on how it's written and my level of interest I suppose. Thing is, I need to know it well enough so that I can run it for a group of fans of it and hit the elements they enjoy about it. Tricky with a setting I'm not familiar with. Easy for a universe I've had 40+ years of enjoyment with.
In conclusion, I think this is why I gravitate toward IP RPGs or feel the desire to homebrew RPGs based on known franchises. Information on them is readily available, familiarity has trickled in piece by piece over time, and the look and feel of the world is shared by all those familiar with the brand.
Given the number of hours in a day, days in a week, etc. that I am able to devote to my hobby (just look at the lack of posts on this blog over the past few months - this has been a BUSY year) it's nice to have the ground work not only done for you, but done in a way in which the players are on the same page.
With an RPGs original setting, any given player and/or GM only has as much info as the books they bought and had the chance to read. This can result in the infamous situation of the players really excited to play that special splatbook class that the GM never even heard of.
What about you? Any feelings on the subject?