I think it's because most the glitches that are used in Minor Glitches runs aren't that hard to pick up and learn.
Don't get me wrong, they'll take some practice, but I just don't think they take enough effort to learn for a good chunk of the community to want a No Glitches category.
Most minor glitches are pretty easy though..
Superspeed - Press two buttons at the same time Spindash - Press two buttons at the same time Itemdash - Press two buttons at the same time Bomb Jump - Put Link and a Bomb in the right spot (plenty of guides!) Fake Flippers - Put Link in the right spot and walk (plenty of guides and easy!) Mirror Block Erase - Push a button while you walk Keydash - Have Link run at a door from a certain spot
^ this is mostly true, but to clarify:
A spindash is pressing a button the frame after releasing another button.
It's also somewhat difficult to define what is truly a "glitch" in this game and what is just abuse of game mechanics. Some of these glitches are version-specific, but some are not. Generally, these minor glitches do not sequence break the game in a significant enough way to consider banning them for the main category. However...
There's nothing preventing anyone from running a truly glitchless version if they so desire. Its lack of presence on these leaderboards has no bearing on what runners can/can't do. If there's enough interest in a category with a clear goal and definition, and enough people start running it, more than likely a leaderboard would be created for it.
I run on 1.1 so I can't do most glitches, the only thing I do that I would consider a glitch is the torch glitch on ganon. I would not classify bomb jump or key dash to be glitches.
Glitchless categories are fun, even if the glitches are "easy" to learn and perform... I mean, some players just want to find routes to complete the game fast enough without depending on glitches that some dislikes using to finish a game