However, it makes learning to read and speak other languages particularly effortless. Mind you, it doesn't teach you grammar or definitions or anything of the sort, but it is a universal way to describe sounds, regardless of language.
Most dictionaries have their own phonetic system in place rather than simply using IPA. I don't understand why the don't just switch.
Maybe if you’re trying to gain or get rid of an accent, or trying to understand why native speakers are telling you you’re doing it wrong, but it’s bonkers useless for learning to speak compared to just listening, and it’s equally useless for learning to read because only reading the actual language will really teach you to read the actual language.
IPA can be fast shorthand for a linguist to conclude, for example, “ah okay, so in Korean aspiration rather than voicing distinguishes these phonemes” but for Babby’s First Korean Class that’s still going to take explanation. Assuming in your scenario people have mastered the whole IPA (which I don’t consider very realistic even if it is noble), there are still certain things about languages (such as allophones and how they are treated) that are basically outside the scope of the IPA on its own.
And a lot of dictionaries (being digital these days) have IPA as an option, so I don’t doubt that in 50 years’ time dictionaries will be using it anyway and people won’t be uncomfortable with it as a pronunciation guide for their own language. They don’t “just switch” because it takes time for people to get used to change, probably. In English, I’m sure most people who consult a dictionary for pronunciation want to get in and get out; IPA does not help them out there very much.
It’d be nice if everyone could be an academic linguist, but... let’s have everyone use their own language well first and foremost. That is in itself a difficult task.