Well that’s the question
"Just asking questions" is not a plausible defense when the question is this leading. It's like asking "Is women being dumber than men possibly linked to lower testosterone?" and claiming that you are just being curious.
Why would this be unlikely? I'm struggling to think of a cause that would result in both a constant rate of these things AND a rate of several percent (de novo mutations aren't anywhere near common enough to get you constant rate given that gay uncles arent going to be doing 2x as much parenting as fathers and theres only like 40 mutations per generation).
There's also the evidence of people answering "yes" more to "Are you a man attracted to men? Have you had sex with men?" type questions. Yes, there are other explanations like people being more comfortable answering yes, but it's still evidence.
Also, given the huge stigma associated with both until extremely recently, a significant increase in survey responses has such huge confounding factors that it's entirely irrelevant. There are even today numerous people living in heterosexual relationships unhappy with their sex life and not realizing, or daring to admit even to themselves, that they are in fact gay.
Since gayness is prevalent through the animal kingdom, one of two things must be true: it either helps in group environments (whether you choose to interpret that as group selection or "selfish gene"-style counterintuitive effects) ; or perhaps genes related to gayness happen to be deeply tied to some other very important genes that get easily passed on.
Either way, what is your proposed alternative? Do you think 6%+1% is too large a number for historical proportions of gay+trans people?
By the way, 1% for trans people seems to match pretty well the number of Hijra people in India (10M+ out of 1.4 billion). Another piece of evidence that suggests these rates are relatively constant across the world in vastly different cultures.
This indeed is something that every gay man knows through experience but I suspect that many straight people may not. In many parts of the world (including many parts of the US and Europe) the majority of men available for gay sex do not identify as gay and are not open about their same sex attraction.