This is a bit of an opinionated answer, for an opinionated question, but here goes.
At the heart of blockchain and cryptocurrencies is the want for decentralization. Decentralization relies reducing the need for trust, and reducing overhead.
For example, if you wanted to do this using a regular payment system, you would need a third party to handle transactions (whether it's Paypal, Mastercard, a bank, or whatever). This would increase your overhead, because you now need to pay the third party (essentially through transaction fees). However, it would also requires you to trust that third party. Now, for large institutions like Visa or Paypal, this isn't really a big deal, however, in a societal sense, blockchain technology has the potential to remove power from these large institutions and make more things possible at a grassroots level.
Right now, it's a little cumbersome to use. Most people do not own eth for use as a currency, it's largely speculative at this point. But in the future, if eth really does take off as a true currency, then it will not be a matter of going from USD->eth->services, and then the seller converting from eth->USD, people will spend eth as they would any other currency.
TL;DR - We're in the early stages of blockchain, and people are testing the waters. As it matures, it has the potential to create a new foundation of commerce that moves away from the mega-corporation economy we live in today.