i hate saying this, but Rick was just trying to avoid a harmful stereotype that many of his readers expressed after Nico's whole coming out (they thought bc he "had a crush" on Annabeth that his sexuality was like a cop-out) and it's a HORRIBLE stereotype. my own sister thinks that im bi because "none of the guys at my school have asked me to homecoming" and i'm willing to bet tons of other kids have families who think that too. So Rick made a lesbian couple with less a chance of being hated on.
People have said this before but the best way to avoid a bad stereotype isn’t to just avoid making the character a lesbian or bi (that’s lazy). The only way to avoid making a character a bad stereotype is to subvert it (For example, he could’ve had Reyna say ‘oh I don’t think my attraction to guys has ever been real’ or ‘oh I’m attracted to more than one gender because I’m bi’). If he thinks Reyna’s straight then fine whatever, I disagree but oh well it’s not the first time, but he should’ve left the whole stereotype nonsense out of it. As I said though many people have already said this, so please actually read the posts that you see.