Why do people call the microphone with that name instead of macrophone?

microphone coined from Gk. mikros "small" + phone "sound" (see fame). Modern meaning dates from 1929, from use in radio broadcasting and movie recording. Earlier, "telephone transmitter" (1878) and "ear Trumpet for the hard-of-hearing" (1683). Of the two spellings of the short form of the Word, mike (1927) is older than mic (1961).

So they call it micro-phone due to the fact that it will record/trasmit even the smallest of sounds.

Macrophone has recently been coined by persons in the (voice over IP) field or VOIP as (a large sample of a recording or transmission).