This is something I first noticed about a year ago, give or take. Like, I’ll say “the sky is purple” and someone will respond with “it’s blue?” Why do people do that?
It’s such a strange thing for me, because I’m used to question marks being used for questions, not statements. It feels like at some point, I accidentally fell into an alternate dimension where this is considered a normal use of punctuation.
I know English is a continually-evolving language, so things like this shouldn’t be unexpected. Even still, this development feels bizarre to me.
I think it’s just typical evolution of language, which happens pretty rapidly, since each generation likes to distance themselves a bit from their parent’s generation. It saves a bit of typing, and since typing is such a common activity, it makes sense, just like using ‘u’ instead of ‘you’.