Because the last Bowser Door opens at 70 Stars. If you don't have 70 Star, the door won't open and you just can't access to the endless stairs. You can go in Sky if you do the 0 Star TAS BLJ. That's why there aren't 0,1 and 16 STar Leaderboard

I wish the creator made a custom version for unlocking bowser at 16 stars, it would be fun to see the type of routing and the rng

also, no need for a 16 star run when all you need is 1 death to spawn you in tippy lol