I don't know of too many cases of people lying for brownie points. But let's take Rebecca Sugar for example. She says she's a bi woman, but she's been in a relationship with Ian JQ, a man, since they met in college. That means there was a very small window in her life where she would've ever dated a woman, probably 4 - 6 years between high school and I'll give some leeway after or before that.
That would mean Sugar only ever had to feel the pressures of having people eyeball her for her lesbian crush during high school now and again for a few years. Then she hooks up with Ian JQ, and never really has to go through that again.
Is someone like that valid for speaking on behalf of gay people's struggles? Hell, she probably got more prejudice from her interracial relationship than wanting to go on a gay date in high school and her dad got upset or whatever (I'm making that scenario up, obviously).
Something just feels very disingenuous about her saying her bisexual experiences shaped Steven Universe when that was a very tiny portion in her overall life and she hasn't engaged in it since she met Ian about 15 years ago.