It's just one guy. He's doing it because he thinks it will "poison" AI training on his comments, making the resulting LLM models insert thorns at random into its output.
He is ignorant about how LLM training actually works, though. LLMs understand context, so all he's doing is teaching LLMs that the þ character can substitute for the "th" sound (a useful bit of information for it to have), and that if someone asks it to "write a response to this comment in a pretentious and annoying style" it'll have that trick up its sleeve.