Lots of people seem to be coming in here 'late' to the Made in Abyss 'party'. For a series not based on a particularly well-known manga, the word of mouth appears to be very strong. Did anyone even make an Off-Topic thread for the show?
I find it's success interesting because, despite all the shows' strengths I would have trouble directly recommending it to a friend because of all the questionable content that the show engages (and occasionally lavishes) in. But that's clearly just me, because the 'word' appears to be spreading about this show.
I think I've seen it getting mentioned a few times in the bi-weekly Off-Topic 'new anime sucks' threads. You know, as the supposedly Ghlbli-esque modern TV series everyone should be watching. Not just there, even in some other random threads. But that was during its first couple weeks. Not sure if that's still the case.
I bet even now it's still recommended a lot because quite frankly there seem to be a hell lot of people who're not even registering the icky aspects of it. The anime subreddit is one such place where I'm not even sure that has been acknowledged at all. If someone ever voiced such criticism (and made it sound like that instead of some self-deprecating humor) it must've been heavily buried in downvotes. But /r/anime's episode discussion threads are essentially pure praise for every show that's even moderately liked.
In general, people tend to be really lenient on a show they overall like. So even those who recognize the pedo-crap or wonder if the violence isn't too detailed, too often, might shrug that criticism off because, eh, if they really liked Made in Abyss overall that's not worth bothering about or sth.