I think the reason why is because you're constantly rushing through everything in the levels and don't really need multiple people to assist.
I believe that the moderators are the only people who can add categories. You'll have to hope that they approve of them and choose to add them.
I do agree that not many people would run those categories, but Heroes in Another Dimension S-Rank, All Big Pieces and Switches, and Crown% all have 3 or less runs. I'm not saying that those categories shouldn't exist, in fact, I still think they are more important than level leaderboards, but there are multiple categories that don't have a lot of runs themselves. But that's just my opinion at the end of the day and I'm fine if we don't get level leaderboards. I'm interested in hearing everyone's opinion on this.
Although I do think Demo makes a good point, I think it would be cool to at least have level leaderboards for the 5 levels in Guest Star and the 4 different Dimensions in Heroes in Another Dimension.
Here is a run I did of it just to show what it would be like to run this category. Also I have no experience running Any% so this run is far from ideal.
Kirby is too tired to go and stop Hyness, so he tries to go back to bed as soon as possible. If you haven't already guessed, this category just revolves around you getting the sleep ability as Kirby as soon as possible. The time starts like Any% when starting a new file and ends when you suck up a Noddy (most likely in Friendly Field). This category is just a joke but I'm just curious to see how y'all feel about it.