From my observations over the years it appears to be a combination of making genuinely good and appealing art, shameless pandering, and a good deal of luck.

Ooh I like the first one in this set

What guild is it? I might have to look into it...

I think it depends on what you want from the series. Z1 definitely had better overall writing and executed its core theme better, but I think Z2 may have been funnier, and if you're there to ship Nick and Judy it focused more tightly on their dynamic than the original.

Anyway, have a good end of the year, everyone!