We've had three canon LGBTQ characters in Kamen Rider, but Bravo is the first one that was actually a Rider.
I would guess the reason there are no gay Sentai heroes is because Sentai's target audience is preschool aged while Kamen Rider's is elementary aged, a little older. (Look at the kids in the Kyoryu credits, most of them are no older than 5-6 at the very most.) Given how conservative Japan is, it's reasonable for Toei to expect that parents wouldn't want to have to explain to their toddler about gay people. Even in the west, it would be controversial - can you imagine what would happen if they added a gay character to the cast of Barney, for instance?
Also, notice what Pierre, Luna Dopant and the donut manager have in common: they're all "okama" types, which is pretty much the default image in Japan of a gay person, and they're all older than the main heroes. Toei likes to cast hot young actors as Rider and Sentai leads because they're so marketable, and putting one of them in the role of "the campy gay guy" wouldn't sell so well. Kamen Rider usually has a bigger supporting cast, so you can get away with a Kaba-chan or a Metal Yoshida, but not so much in Sentai where the focus is on the main team. I find it unlikely we would ever get a lesbian character. It's still rare to see them on Japanese TV, and Toei puts a lot of effort into selling Sentai and Rider actresses as idols, so the characters have to be seen to be "available" to men