I want to suggest that there are recent reasons why Tesla, as a brand, has specifically gotten a bit less popular that are unrelated to the entire EV category. (It's Elon. He's the reason.)
That said, to the extent the result holds true for the entire category, I'd suspect it's because EVs are still fairly immature. It's like "resale value of desktop PCs falling rapidly" back in the 90s, when the field was advancing quickly enough that buying used was genuinely a bad idea.