The quality has tanked in the past several years in large part because of how big it is.
What I think happened in the past several years was the rise of the mobile user.
It’s somewhat hard to write well on a touchscreen and the 13+ demographic expanding as younger teens had less tech-hesitant parents means that low-effort submissions really took off. They don’t write well at all, and they don’t care about paragraphs, punctuation, or using any capital letters.