See the last post in this thread. There have been many discussions about this in the last few weeks.
Popularity has nothing to do with it. It's more about the length of the game that takes to complete in a casual playthrough. If we must generalize, a game that takes less than 10 minutes to beat casually has a lower chance to be accepted than a game that takes about an hour to beat casually.
Oh, it's a life simulator. IIRC simulator-esque games go under heavy scrutiny when requested. So I guess that might be a contributing factor.
Not necessarily. Game requests aren’t approved in a vacuum. A longer run doesn’t automatically guarantee a game is accepted, nor does a game with a lot of downloads guarantee that it’s accepted. Games are judged against a number of factors including the content of the game itself. For example, Doki Doki Literature Club is a very popular game and has (I believe) a decent length to it. However, it’s a virtual novel and those types of games aren’t allowed on the site. That’s just an example, but you get the idea - game requests aren’t black and white, a lot of factors are considered.