It's unfortunately that games with thriving modding communities are so few far between these days. So many fantastic games have branches off of GoldSrc, Source, Starcraft, WC3, Quake, etc. Nowadays it's mostly just Minecraft left.
I do wonder if it has to do with game making tools such as Unity becoming so much more prevalent. I'm guessing most people have just migrated to making their own indie games instead of making mods for other games which is much harder to monetize and scale.
Although I guess there's a resurgence of game creator games. Dreams [0] and Crayta [1] specifically. Very reminiscence of Gmod and the like.
For one thing Minecraft absorbs a lot of this interest. I'm not going to check out your new mod for some game I don't own and which has no other notable mods, but I might check your Minecraft mod, and I definitely will play it if it gets bundled into a "pack" I was interested in anyway. I had no particular enthusiasm for a mod focused on rats (plague rats, rat breeding, rat training, an entire rat civilisation including terrible rat-based puns...) but it's baked into MC Eternal so now I have a cage full of tame rats and a hankering to find Ratlantis.
The choice of Java for Minecraft really matters. Java's if-it-compiles-it-probably-runs approach means third rate programmers can easily put something together that doesn't crash the game mysteriously every five seconds. Java's strong OO background is well-suited to modifying a game too, and particularly to allowing mods to be compatible with each other.
Constraint is often helpful in art. Few of us have the grand vision (and sufficient free time) to build a sprawling Total Conversion that radically overhauls gameplay, visual style and so on. So if you're thinking smaller then something like Super Mario Maker 2 looks pretty good. Can you put in weeks to make something as fresh as the Mario "ROM hacks" made with Lunar Magic (software to modify Mario) which Nintendo won't admit inspired SMM? No. But you can spend a few hours arranging pre-existing components to make something pretty interesting within Nintendo's agreed constraints. Or you can spend five minutes adding every possible boss character to a single screen fight like a two year old finger painting. Whatever you want.
I would also add IMO the main reason that Java matters: it's easily moddable without the creator's permission. For most of Minecraft's existence, there was zero official mod support and zero in-game scripting abilities. However, Java is relatively easily decompilable and many modders put in effort to deobfuscate it.
The end result is that Minecraft was easily moddable without Mojang needing to officially support them in any way.
I do wonder if it has to do with game making tools such as Unity becoming so much more prevalent. I'm guessing most people have just migrated to making their own indie games instead of making mods for other games which is much harder to monetize and scale.
Although I guess there's a resurgence of game creator games. Dreams [0] and Crayta [1] specifically. Very reminiscence of Gmod and the like.
[0] https://www.youtube.com/watch?v=rezzjJ4NtK0 [1] https://www.youtube.com/watch?v=ZTo8TiOoABk