They do it to annoy you. Just you.

Autocorrect seems to have gotten noticably worse for me in recent years. I regularly find that the entirely correct words which I type out get changed to something completely different because the autocorrect decided that I couldn't possibly mean that word. It regularly helpfully replaces entire words after I hit space and have moved on to the next. By that time, I'm usually focused on the next word, so slip-ups that I almost never make at a dumb keyboard (like its vs. it's, there vs. their, your vs. you're, or were vs. where vs. wear) happen with shocking regularity unless I proofread the entire comment. As a perfect example, I had to proofread and fix multiple instances of such while typing those examples.

Probably they’re swiping on a phone keyboard and autocorrect fucked them, or they’re using text to speech and the diction fucked up and they didn’t proofread it.

If type like sound in head, where and were same. And type learned enough not think about every letter.

I can't speak for others, and I'm not sure I ever make that particular typo (espec swipe typing on phone), but I've noticed that I sometimes make typos that don't particularly make sense to me... I'll write a similar word that I would never actually confuse with the word I wanted...is not a homophone, is not a letter adjacency typo. I think the brain just works differently than we expect sometimes...