I know they like to be picky, to separate the “lifestyle hipsters” from the people who really want to become a monk/nun, after all, it is shared living with a lot of other people, so it makes sense to pre-screen a bit harder than your average student dorm. Plus, it is (meant to be) a (mostly) lifetime decision, so them making it hard is probably seen as a favour to weed out the ones that really should not do it.

But other than time, dedication, and maybe no felony record for setting churches on fire, I don’t think it is really meant to be “difficult” as in “we only take the best”.