Well, Gallade and Froslass’s evolutions are determined by genetics, as noted here: http://bills-pokedex.tumblr.com/post/149893951891/a-recent-ask-about-gallade-got-me-wondering-why
Salazzle is a bit more complicated, and it’s actually far more interesting. You see, one of the hallmarks of a salazzle is her ability to attract and enrapture male salandit. She does this through the release of powerful pheromones, which are emitted through scent glands located under her tail and on the red markings in her chest.
The reason why I bring this up is not because these scent glands are directly responsible for a female salandit’s ability to evolve. Rather, they’re directly responsible for the males’ inability to do so. To put it in short, these scent glands are present in female salandit as well, and although they are far from as powerful as a salazzle’s collection of glands, they still do the job just as effectively. Between salazzle and female salandit, male salandit often find themselves at the beck and call of half their species for the majority of their waking lives. They’re compelled to expend much of their energy building nests for and protecting females (as well as their eggs), and much of the food gathered by a reverse harem of male salandit (that is, incidentally, the actual, scientific term for it) is given to nesting females. Consequently, male salandit often lack the energy to evolve, if they’re not simply too underdeveloped from malnutrition to do it.
Of course, one might ask if it’s remotely possible for a rebellious male salandit to achieve evolution, but I’m afraid there are two issues with that. First, while it’s true that there might still be outliers, it’s widely believed that the salandit species has gone on this way for so long that male salandit actually lack the ability to evolve on a genetic level—as in, they lost their ability to evolve via adaptation. Second, even if they hadn’t, a female salandit’s pheromones are much too powerful for a male to resist. And to those of you who question how one can be virtually incapable of dodging a request from someone with whom you’re thoroughly in love … try rebelling against your significant other when they ask you to put the wet laundry in the dryer. See how well that goes for you.
Bill, can you really make that kind of claim when you haven’t dated anyone in years? —LH
Of course I can. By the way, your shirts have about ten minutes to go, and you’re welcome. —Bill
…this is one of those times when I try to be clever and realize all too late that it went horribly wrong, isn’t it? —Bill