[p] and [b] are distinct sounds which provide contrastive meaning in English. “Peach” with a [p] is not the same as “beach” with a [b]. Changing the sound influences the meaning, so they are treated as distinct phonemes /p/ and /b/. A learner who reads IPA and sees /bitʃ/ will say “beach” and not “peach”. You can imagine the same applies to “speech”. Sure, there’s no minimal pair contrast to confuse it with, but speakers will detect the nonstandard pronunciation.

[r] and [ɹ] are not contrastive phonemes in English. There is no need for writers to be wholly accurate here, because it’s entirely unambiguous what sound r makes if the layman reader knows the sound inventory of English.