This is a fallacy, in that it presents false reasoning.
No significant proportion of the audience is buying non-erotic-focused TTRPGs, videogames, etc. for "sexy art" as were. However, that does not in any way mean that such creations should not have "sexy art" in them. There's an underlying prudish sentiment that's being taken as read, taken as common, when it actually isn't. This idea that media/artwork is either "sexual" or "not sexual". That there's some thick and obvious dividing line, and the related idea - a very American Puritan one, that it's dangerous or wildly inappropriate to expose people to anything "sexy" when that wasn't the obvious focus of the product.
To be clear, I'm not suggesting you're personally a prude, but the
idea that unless an RPG is "dedicated" to the erotic, nothing "sexy" should be depicted in it is absolutely a prudish and puritanical idea, and rather culturally specific to the US (albeit disturbingly common there).
The reality is, unless the book is specifically aimed at children, it's probably fine for the artists/creators who make it, to include some artwork which some people will regard as "sexy" or "risque" or whatever. It's not required that it be included, but equally, the idea that it shouldn't be included simply because the RPG isn't "dedicated" to that is a faulty one.
This is important to me because it's a fundamental artistic freedom, and honestly a lot of good art involves an element of sexuality or sensuality. And when people dislike that, or just want to draw lines around what is "okay", it also (surprise surprise) tends to be LGBTQ+ sexuality/sensuality that gets picked up and kicked out first.
Specifically I'll be sad if all/most TTRPGs end up like this -
Everyone Is Beautiful and No One Is Horny - Blood Knife
I know I'm extending a lot from a short post, and I don't expect you intend prudishness or the like, but I do think you're illustrating a poorly-examined/unreflected bias that's unfortunately increasingly common today.