This isn't a qu-- actually you heard that already (˃ . ˂˶)
I can definitely attest to the culture, which is fresh air compared to a lot of networks (e.g. that Draw a Duck post is probably far beyond a lot of platforms' capabilities/proclivities)
I think some of it boils down to:
The Lemmy Algorithm. This is a big flaw with Reddit -- people have the attention span for the first ten comments, and then subcomment upvotes halve (with decent std. dev -- we aren't Zipf's Law devotees there) until invisibility. I don't think my Reddit comments are even seen, let alone replied to. But here, new comments have a chance.
The sense of "mineness". As another here said, there's responsibility to raise your communities right, and another to interact (hence, variably lower hostility). I don't post much but I respond a lot to the people who comment in them, because I feel that I have to contribute to keep this sanctum humanly alive.
At risk of sounding self-absorbed/elitist, the entry level. People are here because they were dissatisfied with the state of other sites, then made a jump; this is a sieve that to an extent increases the standard of sorting by new. (This has limitations of course, and it isn't necessarily advocating for Lemmy to never be mainstream.)
Btw I think a post like this would be better suited for [email protected] (not saying to repost there now) or a similar discussion sub ദ്ദി(˵ •̀ ᴗ - ˵ ) ✧