Why wasn't the Buddha a solipsist? Don't get me wrong, I'm not asking because I consider myself a great person etc., Chakravartin, but why didn't the Buddha take solipsism seriously, perhaps before his complete enlightenment? If he's so great then how can it be that we, everyone else, are so little?

Was it, perhaps, because he was born a prince, or there was no history of solipsism in India at the time, or what, really? 

I think it could just beyond the powers of imagination to get inside a mahasattva's head, so to speak.
Solipsism is an extreme opposite of Buddhism. It posits that only the self is truly real. That all that exists is the self. It places the self on a throne.

The Buddha was not a solipsist because he saw and knew the truth: that the self is not real, but rather like an illusion with not one iota of real or inherent existence. Seeing the truth, how could he possibly believe solipsism?