It's not exactly because they are not "open" to it. It's because Glitchless on its own is simply very hard to define. Just throwing in a glitchless category on the boards and call it mod discretion is not going to work. Without a failproof concept it's a recipe for disaster and it's better to not add things before proper consideration and preparation. That said, the game hasn't even been 2 weeks out yet. Leaderboard aspects are subject to change. NMG or Glitchless categories will likely also be considered. Give it some time and patience.
To add to what Daravae said : categories exist on leaderboards because there are people behind them to route and run them. That is to say if no one route and run glitchless, the category won't have any reason to exist. That is also to say : it's not because a category doesn't exist on a leaderboard that you can't run it for the sake of it ; If you wanna run, idk, no-dash% for example but the category doesn't exist, you can totally route it and run it for the fun of it. And who knows ? If the run is actually fun and other people start running it, maybe the category will be added ?
I would say glitchless category would definitely be nice since the playstyle is very different and we get to see stuff we usually don't see.
Recently a vote on the MDSR Discord has lead to the timing rules for Individual Levels and Master Levels being changed. In the upcoming week or so, we will be cleaning up the IL and ML leaderboards to match with the new timing rules, Old runs that do not comply with these rules or where the video su