Uh, actual porn consumption would wildly disprove your "97%" assumption. The fact is that most people who consume porn with trans women, including content where trans women top, identify as straight men, and that content is produced by a lot of mainstream outfits these days and constitutes a significant part of their catalogue. Also, gay men are overwhelmingly (this would probably actually fit your 97% number) not into trans women at all. Shocking (not really), but true.
The problem is as
Hungover00 indicated, that a lot of the time futa and trans content gets bundled with a bunch of other stuff that people who would be ok with trans content might not be into, like femdom (and futadom as its own entirely different category with all the third gender work out there now), humiliation, slave content, forced feminization, and other hard kinks that are entirely tertiary to the futa/trans content.
Also the thing with the futa-on-male people is that they are extremely adamant about that content. You can look at the bigger futa-on-male games and see that they generally have a consistent and persistent base of support. However, none of them is nearly as big as the biggest male-on-futa game, which is Twisted World. This is a situation where you have an actual, factual vocal minority, and they very much would like to be catered to. To be fair to them, they do spend their money to support good content of what they like.
Personally, I'm a fan of switch content with a masculine straight guy, and whenever I say that a lot of people seem to indicate that they are too. You are just never gonna encounter people rabidly agitating for that content, and that might lead you to think it's less popular than it is. Also for some reason most vocal people are fans of strictly futa-on-male or male-on-futa, and they tend to but heads with each other for some reason...
But also, most devs don't even make actual good trans characters. The few titles with trans characters (as opposed to futa as a an entirely fictional category) that are believable tend to generally be well received in terms of their implementation, especially if they're optional (generally polling on including trans characters in games with masculine male MCs tend to have 30-45% of people in favor of it, so it's not as controversional as some would have you believe). You can see Parental Love/Apartment 69 by Luxee, Depravity by Dante (he doesn't update often, so he's lost a lot of support over the years... same with Luxee recently, actually...), S.H.E.L.T.E.R. and Stellar Dream by Winterlook. Those are the ones that are easy for me to remember, there are others.
For example, Nenad Asenovic had a game with 0 futa/trans characters whatsoever as his first game, and Patreon polled on including some in his second game (this poll was for paid subscribers only, so no brigading or pollution) and I think the final tally was like 40% or so in favor. I'm not a patron of his anymore so I can't pull it up, but yea having optional futa/trans content is not gonna drive droves of people away. The people who are scared off will probably be very loud about it though.
God, I need to learn to get my points across with fewer words, but I'm trying to provide a comprehensive view of the topic here, lol...