The issue is not storing the data, just like "email" doesn't store data. It's just a protocol and a data format. This makes it interoperable across whichever industry player wants to spring up and compete for your service.
Ex:
Don't like gmail? Go to ProtonMail. And you don't lose the ability to interact with people who do use Gmail.
Don't like Facebook? Go to Ello. But now you've lost your entire network.
The decentralized web will be built on data formats and protocols that allow you to take your data with you and force companies to compete with the quality of their service, not the size of their network.