One thing that always surprised me about navigating this fetish is that most women who are into it say they first found it out from a boyfriend. Like around 75% I've spoken to discovered it that way. Take girls like CandiKayn, for example, who were thin up into meeting FA boyfriends, but then embraced their man's kink and enjoyed it. Many such cases of this. This is very different from most dudes I've known who are into it, who have just always been into it.

Not to get too redpill biotruths, but I wonder what the implications of this could mean from broader male and female sexuality. My belief is that women just have much more "fuzzier" sexualities that remain very adaptable and flexible late into adulthood, whereas male sexuality is more firm and unchanging. Does this ring true to anyone else? What mean?

There might be truth in this, but I think it's dangerous to jump to conclusions and other factors should be considered.

One potential confounder (feel free to correct me if I misread your post) is that you're talking about two different preferences: men who are fat admirers and women who enjoy putting on weight or being fat. How do those numbers compare when it's male FAs vs female FAs? Or men with a gaining fetish vs women with a gaining fetish? Maybe it's people who get turned on by putting on weight that are more fluid with their sexualities?

Also, what's your sample size? How many people have you talked to, and in what setting? If, for example, you spoke to most of the women using a specific dating site platform, it could be that women with more fluid sexualities are attracted to that platform and that could skew your results.

Not trying to dump on you OP, I just want you to consider all possibilities.

The ones that don't get into the fetish to make money are usually motivated by the desire to gain male approval/attention. Without one of these factors at play, they would just find a single feeder to fund their gain privately. Though most have feeders who encouraged them to start selling content in the first place lol. The most business saavy will pretend they're single, though - and make it seem like their feeder isn't involved.

Wikipedia has an article on Sexual Fluidity that bolsters the redpilled biotruth that female sexual orientation is more fluid than male. Excerpt related:

"While stability may be more common than change, change in sexual orientation identity does occur and THE VAST MAJORITY OF RESEARCH INDICATES THAT FEMALE SEXUALITY IS MORE FLUID THAN MALE SEXUALITY. This could be attributed to females' higher erotic plasticity or to sociocultural factors that socialize women to be more open to change."

Though the research is more focused on fluidity between hetero and homosexuality, I think it may be relevant here.

female FA here, i've been into it as long as i can remember, but i've definitely given into other kinks for partners. i wasn't into bondage and rough stuff until i met a boyfriend who was. now i associate it with providing my partner pleasure, which i like.