They use Bitcoin due to its granularity (1 Satoshi = 0.0000040352 USD) and because users can mine a small trickle of new money easily with the hardware they have designed. But mainly because it's much easier than bootstrapping users onto a new payments network from scratch.
Yes, you could design a new micropayments system denominated in dollars with electronic wallets that would piggyback off card and bank payment networks, but you would add latency in flushing (admittedly negligible) amounts to your bank, and if your service became large enough, credit card providers would probably disallow you from using their infrastructure to deposit billions of tiny amounts into micropayment wallets, which would generate a lot of overhead and fees for a relatively small transaction volume.
Seems to me that the reason this micropayment startup doesn't exist is because it wouldn't solve any pressing problem at the moment.
Yes, you could design a new micropayments system denominated in dollars with electronic wallets that would piggyback off card and bank payment networks, but you would add latency in flushing (admittedly negligible) amounts to your bank, and if your service became large enough, credit card providers would probably disallow you from using their infrastructure to deposit billions of tiny amounts into micropayment wallets, which would generate a lot of overhead and fees for a relatively small transaction volume.
Seems to me that the reason this micropayment startup doesn't exist is because it wouldn't solve any pressing problem at the moment.