Not this ignorant myth again - it isn’t a new word, been in use since mid 60s. A transpiler is a form of compiler from high-level language to high-level language. A compiler didn't even originally translate, but just link.
The same way ‘navy’ is a kind of blue but we can say navy and add a little more specific information. Nobody rails against navy saying ‘but it’s just a shade of blue!’
> Also why do people invent a new word 'transpile', when the old word already perfectly describes translating from one formal language into another?
The answer is... the old word ('compiler') didn't mean what it does today, back in the 60s, when 'transpiler' was coined. Compiler with its current meaning isn't a much older word than transpiler - they're near contemporaries (50s and 60s). Before that a compiler meant a linker.
Your criticism doesn't match up with the history.
Of course, if we had more rational vocabulary, we'd call them 'translators' instead. (In fact, that's what German does. Perhaps they coined their corresponding term a bit later, when things had already shaken out a bit more.)