The technology ratchet
Any useful technology that's successfully adopted by a culture won't be abandoned. Ever. (Except by top-down force).
The technology might be replaced by a better alternative, but society doesn't go backwards.
After books were accepted, few went back to scrolls.
After air conditioning is installed, it's never uninstalled.
Vinyl records, straight razors and soon, drivable cars, will all be perceived as hobbies, not mainstream activities.
This one-way ratchet is accelerating and it's having a profound effect on every culture we are part of. As Kevin Kelly has pointed out, technology creates more technology, and this, combined with the ratchet, has a transformative effect.
In a corollary to this, some technologies, once adopted, create their own demand cycles. A little electricity creates a demand for more electricity. A little bandwidth creates a demand for more bandwidth.
And the roll-your-own media that has come along with the connection economy is an example of this demand cycle. Once people realize that they can make their own apps, write their own words, create their own movements, they don't happily go back to the original sources of controlled, centralized production.
The last hundred years have also seen a similar ratchet (amplified, I'd argue, by the technology of media and of the economy) in civil rights. It's unlikely (with the exception of despotic edicts) that women will ever lose the vote, that discrimination on race will return to apartheid-like levels, that marriage will return to being an exclusionary practice… once a social justice is embraced by a culture, it's rarely abandoned.
Fashion ebbs and flows, the tide goes in and it goes out, but some changes tend to flow in one direction.