Most programmers are only semi-literate; they never learned English well in the first place.

Things like word order, natural language flow, and the basic concept of structuring code like well-written prose doesn't occur to them, because they can't write prose to begin with.

It's all just a string of wierd symbols to them: 'u','n','l','e','s','s' is more characters than 'i','f',' ','!', and thus harder to understand.

I'm no grammarian, nor do I claim to be good at English, but I can't count the number of comments I've read that don't even start with a capital letter, let alone clearly explain the topic at hand. :-(

It's not just foreigners, either. :-( One native speaker who I worked with wrote endless run on sentences fragments, which were often self-contradictory. He capitalized things randomly.

When you don't know what readable prose should look like, everything looks equally readable. :-(