this is because homestuck is fundamentally about women & lesbians. i hope this helps

on a more serious note i genuinely just... don't think your logic is sound here? davekat is extremely well established even if theyre not making out on screen, and have like... way less canon relationship issues than rosemary. you could make the same argument that homestuck has a difficult time dealing with sapphic relationships since rosemary almost crashes and burns and vrisrezi detours towards m/f pairings and are only able to succeed in a literal alternate timeline.

the epilogues are a different story because its literally made to mock fanfiction. everyone forgets this. dirk is a fujoshi