But mods are afraid to be strict and delete bad-quality posts and replies, because apparently there is a way for ordinary redditors to complain to Reddit, who can then assign the sub to other mods who promise to be tolerant. Corporate Reddit wants people asking the same things again and again, and posting replies regardless of quality, because that means engagement.
* (A good example of this is any post on a mainstream travel reddit asking about travel to Iran. Many tourists go to Iran – nationalities other than the US and UK can get visas, and they overwhelmingly enjoy their time there. For 30 years it has been a common rite of passage for Eastern European backpackers, their first trip outside the Europe–Turkey–Caucasus region. On dedicated travel forum websites, people know this. But Reddit threads quickly amass replies from Americans like “Dude, you’re going to get beheaded.”)
That's not quite true. Sources are strongly encouraged but not required. However, if you're asked for sources and don't provide them then yes, you will probably get deleted. [1]
In practice, it's usually pretty obvious which replies aren't going to be able to back themselves up, and they almost always fail the "in-depth" test too making it a moot point.
[1] https://www.reddit.com/r/AskHistorians/wiki/rules#wiki_sourc...
It doesn't have to go to the extreme of AskHistorians, because there just aren't enough experts on all the various topics that get discussed here to mandate scholarly monographs in replies, but there's still a lot of room for improvement.
The practical result is mainly seen in two ways. The first is when extremely interesting questions end up with no answers (the running joke is entire comment chains of [deleted]s). But the second is that when a question does receive an answer, it is usually brilliantly and thoroughly answered, with assumed followup questions answered as well. And those posts end up getting linked to by other social media platforms, paraphrased and summarized on websites like Atlasobscura, and plagiarized by clickbaiters.