It's definitely a lot of supply and demand, and it's also a relief that you can finally write about gay relationships without getting a HUGE amount of backlash and spark controversy. Though it's still a thing, it's way less now. People are excited that you can finally make them, so they're booming. I'm sure it'll die down eventually, but it's going to be a thing for a long time coming. Scifi had it's time, fantasy, westerns....every genre has it's moments where it seems to be everywhere. Time for the BL genre to boom right now.
Next, is world domination.