I'm not sure that 'compere' (which according to Google NGram viewer is not completely unknown in the US) and 'MC / emcee' are entirely synonymous.
For example, at the start of a boxing match, the person in the ring with a microphone ('On my left, in the blue corner all the way from......') is an MC, a 'Master of Ceremonies'. Nobody in UK would call him a 'compere', which normally refers to somebody introducing the acts in a variety show, in a theatre or on TV.
Also, over the last thirty years or so, anybody aspiring to be a rap artist has, it seems, been obliged to go by the adopted name of 'MC xyz' or whatever. Although I'm not sure if that usage is ever spelled 'emcee', it may have helped to make the word itself better known.