
Yap session ahead.
To my knowledge, the studios don't really choose what to adapt. Most of the time they're just hired to animate. The ones who choose are the producers who often are made out of the publishing company, some rich people sometimes, a streaming service sometimes too, and on occasion people from an animation studio. For example, for a shounen from Shounen JUMP to be adapted, Shounen JUMP itself has to push the anime. They collab with certain people from the industry, decide which studio to hire to animate (if the studio isn't directly involved) and we get either a top-tier animated shounen or a... not so top-tier animated shounen, depending on the studios that were available and the budget they had. But most of the time the publishing company takes the first step because the anime is basically promo. If the anime does well, a lot of fans start buying physical copies of the manga and the publishing company thrives. It's a gamble that sometimes pays off.
I'm assuming a lot of BL and GL publishing companies are very cautious with what they decide to adapt. An average shoujo might still do better than a good BL or GL audience-wise on TV and they need that audience because the more people watch, the more people get exposed, the more people will buy the manga. But we're already seeing a shift, more and more decent BLs are being adapted and I think the change is slow, but noticeable. As long as people watch these BLs legally and buy the manga afterwards, producers will see the demand. It all depends on those people high up who decide which of their titles would benefit from an adaptation. And of course, if a publishing company is small, has little influence, the chances to have the power to push for an adaptation are... well... kinda tiny, unless a rich person sees the potential and decides to invest.

I've read a few chapters in the past, but I decided to wait for it to be complete. It's indeed a great BL and it would thrive as an anime.
I looked it up and it seems that its publishing company is "from RED Comics", a subsidiary of ShuCream which primarily focuses on BL and josei, but unfortunately none of their works got any anime adaptations so far, despite ShuCream being over 30 years old, damn. If that's the case, I'm going to assume they're not that interested in anime. But who knows? Maybe they'll change their mind someday.
I honestly don’t get how average shoujo manga keep getting anime adaptations, while so many amazing BL stories get ignored just because they’re not seen as “mainstream.” Studios are too focused on playing it safe. A gem like Yoake no Uta is still waiting to be noticed. It's frustrating. I just hope things will change and BL stories will finally get the recognition they deserve ╥﹏╥