I worked for a company that offered an unlimited X. A startup used us to host some of their X, and literally uploaded a thousand times more data than any other user.

That is why those things end up in contracts.

Someone is going to attempt to upload a pb of photos to amazon, and amazon is saying unlimited, but for personal usage (threshold quite possibly judged on a case-by-case basis), but doesn't include free storage of pbs of pictures.

At the end of the day, users need to be somewhat reasonable about what they expect from a $60/year service.