To give a little historical context...
For a long time on Tapas, being listed as multiple genres was something only open to premium comics, and it was frustrating because everyone could see the option was there, but not open to us, so obviously, people demanded it. Tapas delivered... but for whatever reason, we ended up with a system where mechanically only your primary genre does anything (probably because this was the easiest way to meet the demands people had).
I get it in some ways, because if you think of it like this:
BL comics tend to average a much higher number of subs and per-update likes than comics of equivalent length and quality, because there are more Tapas users who browse and read BL. This would mean that if a BL was BL/Comedy and listed in both, it would easily dominate the listings for Comedy too, so the top listings for Comedy would all be BL with comedic elements, and if it was BL/Romance, it would go back to the top of the Romance rankings being full of BL, which is what caused the creation of the BL category in the first place.
The alternative, which I've suggested before, and would love to see, is the ability to filter by comics which have certain combinations of tags, and for Tapas to recommend people comics based on the most common tags or tag combinations in their library.... But I know that's not a trivial amount of extra work to implement, so even if Tapas is planning it, it's probably lower priority than things that just generally make the site work better.