why do intro to ling professors insist on not teaching us [ɹ]? why did i learn it as [r] when that’s a trill? We already had to learn that smorgasbord of vowels and diacritics, what difference would teaching us [ɹ] be?
The excuse that my professors often used was that [r] is quicker and easier to write than [ɹ]. I know it seems like a silly thing to worry about when they're the exact same symbol, just rotated on an axis - and if you're learning the whole IPA, there's a whole slew of other symbols that you have to get used to writing, too, so why not add this to the list? But if I'm completely honest, it was true for me. It saved some time for me when I was transcribing speech - especially running speech. And it works perfectly well for dialects or languages in which true [r] is absent. In the end, our professors were conscientious enough to teach us to make clear notes about when we were using [r] in place of [ɹ] when writing academic papers.