Native English speakers write less buggy code? That's a pretty good competitive advantage.

Technical books aren't just about the code itself. Programmers don't necessarily make for good technical writers, and non-native speakers of any language are worse writers on average in that language. Put those two things together, and a non-native programmer writing their first book needs all the help they can get with editing and reviewing the text.

Even a native author will need all the help they can get with editing and reviewing the text. But yes, even more so for non-native speakers.

Oh no, I did not mean to imply that. Just that quality control at packt doesn’t seem to great, so the books contain bugs and typos. The latter probably more if the author is not a native speaker.