[Aloisius]

It reads like textbook mind reading to me.

The author does not actually know why people write with poor spelling/grammar nor truly how others would interpret them writing with with poor spelling/grammar.

They have a guess, but there are any number of alternate reasons why someone might write poorly. They could be technologically illiterate, fat fingered, easily frustrated, mirroring their children, need glasses, careless or any other number of reasons. The only way to find out is to ask.

Engaging in mind reading is fraught with danger. You're more likely to project your own own mood, stereotypes, behavior or beliefs on to others than actually guess what someone's thinking.

[NoGravitas]

I think it's less mind-reading than looking for a sociological explanation.

That said, I think a big underlying cause is that Business Idiots [1] are, in fact, idiots. Even so, it's worth looking for a sociological explanation of why Being An Idiot doesn't hurt Business Idiots like it would hurt the rest of us.

[1]: https://www.wheresyoured.at/the-era-of-the-business-idiot/