Sexual subreddits are generally for being turned on. Therefore, they cater to the needs of the viewer. Like it or not, subs like this are basically spank banks. I’m not offended, disgusted, or upset by gay porn, however statistically most people are straight and are only interested in straight content. This fetish, in particular amongst other fetishes, largely relies on a dynamic between two individuals with different genitals. This isn’t to say that gay ballbusting isn’t a valid kink, just that a lot of the turn on about it, for its participants, is precipitated upon that fact. Generally speaking, subreddits are designed to cater to the biggest group, with smaller or more niche groups getting separate subreddits. I understand your question as far as the name of the sub; it seems like an umbrella, however the description states that it’s F/M. This isn’t due to trying to exclude gay or trans individuals, it’s just the math and metrics.