Guitarists seem to pick up an understanding of music theory (and practice) from other guitarists, which exists at anywhere from 60 to 180 degrees from standard music theory.
Beginner and intermediate guitar music is in sharp keys, to take advantage of the open strings; beginner and intermediate school band music is written in flat keys, to take advantage of the open native key of brass instruments.
If they don’t progress to an expert level, guitarists get very little exposure to flat keys (unless they join the school band); and, if school band students don’t progress to an expert level, they get very little exposure to sharp keys (unless they play in the string orchestra).
At the expert level, all keys are fair game.
Ahhhh! Both of these make total sense, especially when they're learning "cowboy chords" as beginners and most likely from other guitarists.