Presumably because they didn’t study Darwinism at school. Then they would know it’s supposed to be the other way around (and only after mating).
Okay, seriously, that behavior is noted among Montpellier snakes and evolutionary biologists need to come up with explanations:
TS: What is shocking or counterintuitive about these instances of cannibalism in the Montpellier snakes that you reported on? XG: Most of us biologists think that an adult male feeding on an adult female is kind of counterintuitive. I think it probably comes from the fact that the old paradigm was that generally a male would try to mate with as many females as he can to just increase his fitness. The males typically do not take care of the offspring. He is not the one that’s being pregnant. So, for him it would pay off to actually try to mate with every single female he encountered. . . . But recently, in the last few decades, the paradigm has been shifting, if you will, just because we realize that males—they can also be choosy in some ways about the females they mate with.
At first you think it is counterintuitive. And then when we wrote the paper, we just realized [that] in fact there may be many reasons for a male to eat a female. And that could be adaptive—in other words, it could actually benefit the male’s fitness to do that. We do highlight a few of those reasons that we think could potentially explain [these observations].Chloe Tenn, “Male Snakes Cannibalizing Females Present Evolutionary Puzzle” at The Scientist (November 15, 2021)
It turns out that Darwinism can (sort of) explain anything. Even eating the bride before the honeymoon.
The paper is closed access.
You may also wish to read: Can sex explain evolution?