Most open sorce licenses do, not just the GPL. I’m not sure what Minecraft modpackers do. But in the free and open source world, you’ll always find that attribution. Sometimes they have a list who wrote the software and who maintained it for what timespan.
Ah okay. I wouldn’t know. I played Minetest instead of Minecraft. And the community there seems to be nice albeit a bit small. I learned a bit of Lua and contributed some smaller fixes to some mods. But I guess the gaming and modding community for propriety games is a bit different than the open source community.