ive wondered about this for a while, when i research mods alot of the time some stoped getting updated and the cool versions of new ones are too new so you have to just except that the old mods cant be used. It would be way better if we just decided say 1.7 was the modded version, then all mods would exist for that and making your own mod pack with all your favorite mods would be easy, and developers could work on updates instead of moving it on to the next version. I'm sure people have a reason its not done but it seems to make the most sense to me.