[jdmichal]

> I imagine it's because although the sounds are very different cross-linguistically, maybe there aren't any languages where these phones are contrastive and thus they don't warrant separate glyphs in the IPA.

I think this is a pretty spot-on observation. IPA does offer a bunch of diacritics for making more narrow transcriptions. For instance, Spanish's dental <t> is [t̪].

However, the narrower the transcription, the less applicable it is to a language in general. Things like dialectal and even individual differences start to come into play. So in general transcription will only be as narrow as necessary to achieve some point.