If there is one thing users want without knowing it it is the long term accumulation of value.
Writing comments takes only slightly less effort than writing a draft for a book. The Twitter or facebook history, even our comments here quickly lose value. It all vanishes into the hole.
In contrast, i once ran into a geocities page created by a very elderly couple in the US about their vacations. They were old enough to tell the story about how the world changed over time from an appropriately mundane perspective. They probably died before I found the homepage. It was an oddly interesting read. In 100 years it would be truly marvelous.
If the software is there we could probably wrap the proverbial Richard Stallman's browser history into a product worth buying. It would be every bit as funny as it sounds.
I can understand the default not keeping forever, for privacy, storage, and performance reasons.