The issue here is the vast majority of people dealing with cryptos don't know what micro and milli mean. I can't count the number of times people look at me dumbfounded because they can't convert between the amounts because they don't know basic conversion. Anyone who has been to elementary school should already know the meaning of micro/milli, but sadly that just isn't the case. "Bit" takes away this "difficulty" people often have with trying to figure out the values.
I have no problem with bits. Not because I can't figure out the value of the prefix but because I shouldn't fucking have to. mBTC and MBTC and uBTC and yourmotherBTC all have their place, but an exchange should be unconfusing for a trader at first look.