It is way easier to "be your own bank", using free software like electrum or the reference Bitcoin client, than trying to "be you own email" by setting up your own email service and whatnot.

Coinbase or Bitpay are optional facilitators, for people who want to buy or accept bitcins. That is not centralisation, that is just providing a service. Lots of people use Coinbase to buy their coins and then withdraw them to their offline-decentralised cold wallts created in electrum.