Counter-Strike and Battlefield 1942 are two examples I'll call back to as they were two important games of my youth. At the time, most servers for these games were hosted and/or run by people that weren't affiliated with the developers or publishers of those games; it was just something you did so that your local group of friends or community could have a virtual home to get together and play.
My friends and I would have maybe a dozen servers we would keep favorited and a handful that we played on heavily. Over time, you got to know the other people on the server just by playing against them consistently; for example, when BigCheeseburger logged on and was on the opposing team in CS, you knew you had your work cut out for you. There were rivalries and camaraderies that just formed naturally as a result of this. Some of these servers also had web presences with a site that had their roster, dates and times for regular game nights, etc.
Games would also get occasional patches (patching before Steam is something I don't think was better back then) that would bring a new map or two, but that was generally it until a big expansion dropped, like Battlefield's Secret Weapons of WWII pack. If people wanted new content, they made it themselves - I spent so many hours on custom CS maps like Iceworld or even ones that shoehorned in Half Life's terrible vehicle controls to make facsimiles of Tatooine with landspeeders.
In most multiplayer games nowadays, the developer has one or more employees assigned to "manage" the subreddit or Discord for their game. Custom servers are often not even supported anymore, as matchmaking is used to funnel players into full games and keep them playing even if their friends log off for the night. You can forget about creating your own maps unless it's a special case like Halo's Forge mode; the developer/publisher has a great seasonal rollout plan that might never get realized if enough people don't keep playing the game (Say hi to Battlefield 2042!). Players need to see numbers go up so every game has an experience and leveling system first seen in Call of Duty 4: Modern Warfare so that people don't realize how banal and limited the available content is. Cosmetics and boosts sprinkled over a battle pass system layer on top of this as another form of retention.
What has changed in the last 25 years? Games, like everything else, became extremely monetized at all levels, and in the process, conditioned a lot of players to feel that they NEED that monetization or else it's "boring". Look at the reaction to Halo Infinite, a game that plays fantastic but has had limited map/content drops since last fall. Instead of praising the fact that you can ignore its battle pass entirely and just have fun playing a few games with friends every few nights, people are demanding to see their game time rewarded with more progression, more unlocks, etc.