It doesn’t though? There many games for which I use ModDB and many games have modding communities on dedicated websites.
Some of the biggest modding communities (GTA, Minecraft) don’t really use it at all. It’s very popular with TES and Fallout (not surprising considering the original name was TESNexus), but as someone who has spent a very large amount of time modding Bethesda RPGs, many good mods aren’t found on Nexus, even for those games.
I love Nexus. I uploaded 3 mods over the years, and with their donation point system (you get points each month based on unique downloads), I got like 15 free games from their store by this point.
Awesome project, after like 7 years of trying out different compositors, River is the one which made me stick with Wayland.