I think you're spot on with this observation. I think men understand how honesty in this particular fashion works against them as far as preserving opportunity, and I think women are invested in maintaining an altruistic, holier than thou façade when it comes to their desires and preferences, not to mention how often they'll allow other categories and features weigh more than actual physical attraction.
And personally i dont think it's an illogical nor shallow attitude, because I think in practice, the lessening of sexual attraction has a lot more to do with a subject's response or reconciliation to physical changes than the change itself. For example, I imagine women on average would prefer a man with a full head of hair, and would seeing balding in of itself as a bit of a turnoff....unless that man owns that baldness with a confidence that can't be ignored nor not lusted after. Do I think women's weight gain can turn off a man, sure, but I think how women carry that weight both physically and mentally is the difference between "she's gotten too big" and "more of her to love".
I think that's what makes questions like OPs so triggering, people are so invested in making a certain answer be considered so shallow, they completely disregard justification of it lest they implicate themselves. Its easy for a man to say she left me because I got bald or fat, not so easy to admit they let their baldness or fatness dictate the aspects of their personality that she found attractive..Its so easy and sympathy inducing for a woman to proclaim he left because I got fat, older, much less harder to admit she was unwilling to twerk that fat ass and shake them grays as he would've loved because she couldn't get over herself.