Psychologically speaking people like the idea of having a dollar than having a microdollar. Its hard to find value in something that shares the same scale as atoms and molecules.
Yeah, but eventually the metric terminology would become in wide enough use that people would think of a "micro" on the scale that they think of a dollar now. People wouldn't even use the terms "milli" or even "Bitcoin", they'll just say a thousand micros or a million micros.
Sure, 1 million micros equals a Bitcoin, but it would be thought of as 1 million micros, not as a Bitcoin. The holder of such would be regarded as a millionaire.