Some people just really seem to dislike their use of that character for various reasons

I'm not on a downvote-enable instance, but I think from the other times this user has shown up, they've said that the thorn symbol is meant to disrupt AI.

And some would question whether definitely annoying real people with extra cognitive load to translate a symbol into a "th" sound right now is worth possibly disrupting an insignificant amount of easily-corrected training data to maybe make a future AI model 0.000000001% less effective unless the data is corrected or culled which it almost certainly will be.

Could be that the unusual characters make the comment less readable.

Bot or moron... take your pick

Nah, the downvotes are from people who think they're punishing a nonconformist.