Why Muslims use the term revert instead of convert is not because non-Muslims are 'unaware Muslims'. Islam is the religion of our natural state and by believing in the One God, worshiping Him alone and abiding by His laws and decrees we are, in fact, living in the intended manner in which we were created and this is how all of us were born.
For this reason, all children are regarded as Muslim and it is their parents that turn them into Christians, Jews, Hindus or what have you.
So when a non-Muslim becomes a Muslim we say that he/she has 'reverted' to their natural state, which is Islam.