Specifically regarding why Ganon-less runs are a thing despite being a less efficient way to beat the game than Any %:
Ganon-less used to be the fastest way to run the game, prior to more discoveries being made that lead to the current Any % run. Had this not been the case, I would honestly doubt that Ganon-less would have been made a category of its own. Other categories like MST (requiring the player to actually do every dungeon, hence the name Medallions/Spirits/Trials), No Wrong Warp, Glitchless, etc. are just less arbitrary in the restrictions and just make more sense as to why said category would have been made in the first place. But because Ganon-less was an already established route, being the former Any % route, a lot of people just decided to keep running that route.