>Then again, many have opted out of owning desktops and laptops in favor of mobile phones. That also seems terribly inefficient

A lot of people don't need computers in the general purpose sense. I admit my mind boggles a bit when co-workers tell me their kids don't want a computer to do their school papers because their phone is fine. But, then, I'm used to keyboards and what we think of as a "computer" and have been using one for decades--and grab one when I can for any remotely complex or input-heavy task.