I agree with your first comment: a lot of people suck at creating models that are relational. It's also difficult to use relational data outside of a relational system: when you retrieve it from your RDBMS and get it as, say, a Python dictionary. This is the big problem with using SQL for the web.

However, I disagree with your other statements:

(1) we do not have infinite storage. Most data stores keep everything in RAM, and that is pretty limited.

(2) It's really easy to input data into SQL. There are in fact a bunch of methods to do so (almost all still rely on SQL).

(3) (more of a comment, than disagreement) ORM's don't solve much. They just remove the need for engineering a data access API and trade it for performance and cleanliness of code.