might be biased due to being bi myself but imo the simpler/more likely explanation is that the "homosexuality is a choice, reject it" homophobes are mostly bi people who've been conditioned by their environment from an early age to reject the same sex attraction, so it literally is true for them. In private they might also prefer gay porn because they find the taboo aspect arousing (a common pattern that extends to fetishes).

On demographic surveys bi people are much more common than gay people as well, but bi erasure is a thing in both the straight and LGBT community