There is still time for seke.
Because of set yaoi, my friend. Yaoi has its own "rules" and believe me, there are more surprising than expected. From what I've seen when I was in Japan, yaoifans there are obsessed with "categories", set roles (yes, don't forget Yaoi are originally aiming for the Japanese fujoshi/fudanshi fanbase). And more than once, yaoi mangaka who wanted to make their couple sekes had to make DJ through which they reversed the characters' positions. The main one that comes to mind is "Takaramono wa Hako no Nak" (the mangaka reversed their roles in her DJs). Thus, it's really rare to see seke couples in official series. For these latter the only ones I can think of are "Suki Na Hito Hodo" and "Koisuru Futari no Taion" (and still, for this one, it's not obvious and totally official -you have to read the extra chapter to understand XD).
And if you still doubt these yaoi "rules" (that I'd rather call stereotypes/clichés x)) just look at all the fuss Yuri!!! On Ice fans are making about who is the seme and who is the uke. I'm a huge fan of YoI but I soooo don't care who is the seme and who's the uke seriously XD They're a queer couple, so rare in the yaoi universe (got the same feeling as for when I read n.6) For me, they're ust like gay couples you can find IRL (of course, they are some guys who prefer being bottom and others who prefer to top, but honestly, most gay couples are reverse). Anyway, hope it answered a bit your question ^^ Have a nice day~
Don't look at me I'm ugly crying. Brb.