The Dredge Tank

The closest thing to an eternal beauty standard we have is probably to look healthy

What is considered "healthy looking" has also changed several times within living memory alone. Not gonna be rude here, but you're arguing in line with ideologies that try to explain cultural beauty standards away with a superficial and flawed understanding of evolutionary biology that just doesn't hold up when you look at how differently idealized human bodies have been portrayed throughout human history and across different cultures. In many cases, signifiers of beauty where the same as signifiers of wealth and status, and that often included features that can be considered infirm or sicklish (see feet binding in imperial China, before the communists outlawed the practice). Looking healthy often means looking capable of work, and feudalist cultures in particular have frequently glorified to look as if you've never had to work a day in your life because the peasants toil for you in the fields (see also: pale skin in monarchist Europe, something that only fell out of fashion once tans started to mean long beach vacations). And that biologist foundation needs to be pointed out because reactionaries do the same thing all the time, particularly when it comes to their misogynist, racist, heteronormative and transphobic beauty standards. Like, you can literally find similar logic in Jordan Peterson rants, he just does this to fatshame women. Naive biologisms like that are dangerous. It lies at the core of current and historical fascisms to make their agenda against various marginalized populations appear "just natural" and grounded in common sense when they're wholly constructed.

To tie this back to your example, that particular ideal of what women should look like that these people get so incredibly bothered about is that of a culture disciplining women with workout routines and demanding not only beauty, but performance from us. It is the aesthetic expression of girlboss feminism, where you prove your worth as a functional unit of late stage capitalism by getting up an hour earlier for your morning exercise routine. Of course they do not reject that aesthetic because it is pressured on people and loaded up with the expectation to conform to it, or because it expresses a capitalist zeitgeist, but simply because they are treat fiends who spend their entire free time in front of a screen. Which means that fit women who exhibit a high degree of self control and discipline scare them. They demand weak women because of their deeply rooted insecurities and their crushing need to control their partner, and they feel emasculated by a woman who shows the physical signifiers of having adapted to late-stage capitalism and its rise and shine hustlegrind culture. This, ofc, goes doubly when that woman looks as if she could beat them in a fight, and when she shows up in the wish fulfillment treats that are the only thing keeping the hogs alive and pacified, all hell breaks loose.