I've heard that a very high proportion of the economy is sales to businesses, but relatively few people who are thinking of starting a business think of anything but selling to consumers.

I'm guessing it's just that most people have little or no contact with selling to businesses, so it's a blind spot. There may also be an element of preferring to sell an obviously interesting product-- if you're selling to retail, you can still have that, but a lot of business-to-business products are infrastructure.