So the way I see it, when modding became a thing because back in the 90s and 00s, the barrier to entry for a new game was really high, but the barrier for entry for making assets and such was really low. The situation is reversed now-anyone can pick up Godot, Unity, Unreal, etc and start making whatever they can imagine but they can't just start making AAA quality content. That's why you see lots of assets for a few titles where the community has really gone in deep, but also plenty of games that nobody even tries to mod-without the developer tools there isn't much hope, and if you just want the basic gameplay of, say, a FPS building it from scratch is no longer insurmountable.