The transaction process of Ethereum is fast because it is designed to be that way. I do not know what mining algorithm Ethereum network uses but the speed of transaction depends on that algorithm. The cheap transaction fee is a result of the speed. The slower the speed, the higher the fee; the faster the speed, the lower the fee. This is only applicable for the comparison of transaction in ETH and BTC. Think about the speed of tx of ETH as a minimum of 14 seconds and BTC as a minimum of 10 mins. Since ETH miners mines more block than BTC miners then ETH miners could earn as much as BTC miners even though the ETH tx is low and the other way around.