Hi! There's several reasons but ultimately, we just like trying different combinations and this is sort of just what we ended up with for this game (though we understand if that's not a satisfying answer for everyone).
BTMO was originally a side project that ended up becoming our main project after we put our other visual novel on temporary hiatus. Our other VN would have had more evenly distributed LI genders (including multiple yuri routes potentially if we did our side romances the way we initially had planned) and only a single MxM route, which is part of the reason why we did BL-only for Dante's routes in BTMO, thinking we were going to be working on these two VNs at the same time.
Our previous visual novel TCT had 2 fem LIs and 2 male LIs (equal) and one of our other vn ideas we've been brainstorming is also likely going to have an equal amount. We have other amare game ideas with more nonbinary romances, and we even have yuri game ideas! BTMO is just a single game we're working on, and we're not fitting every idea or romantic pairing that we enjoy into it. However, we don't want people to think we haven't heard the feedback and we're going to take this stuff into consideration when planning future games.
If we ever do end up adding more romance options to BTMO (it's not financially feasible for us right now without cutting content from the current LIs), I personally would love to do a free update with another fem romance option for Circe. (In fact, I can think of at least two characters I'd pair her with, though their routes would require some work to fit the main story.) We've only just started working on BTMO's base game now though, so we've got to finish that before we think abt DLCs or anything else.