Some (useless) info about regarding postcreated creatures and pronouns. Firstly, if somebody doesn't know yet, my own language (Finnish) doesn't even have gendered pronouns, and we got this apparently peculiar spoken language where we call everything and everyone "it" while our actual Human Pronoun is used mostly sarcastically, so this as a starting point has caused some issues while learning literally any other language.
Anyway so, postcreated creatures are non-biological and supernaturally functioning in the first place and it's always morally correct to call any of them just "it". They cannot reproduce and most of them are not even at person-level sapient. While "it" is logical in their case, I've never felt calling sapient things as "it" any issue either, because aforementioned weird language perk.
However, yeah, English (that I use as a worldbuilding language and sometimes to communicate with people) works differently. Sometimes it's just annoying while your normal level of gender in language is none, but in this case I've seen it as a funny nuance that adds something to creatures otherwise outed from gender. So, many sapient ones have preferred pronoun even if only real reason behind them is just that I as a creator made them because English forced me to think nuances. But a vast majority of postcreated creatures are just "it" and they don't have enough concept of gender to even think of it.
"Why is that with this pronoun?" I'd say that I just kinda throw mental darts/"ask" them and then get some result, as creatures themselves are not very gendered. They're skull/shape headed oddities, there's no deep logic.
Eventhough I keep joking that Pride is a he because he's kind of dick and Envy is they because I remember all "gender envy" memes...yeah.
