Not "everyone" thought tablets would replace PCs.
I did not, which disproves the "everyone."
As a touch typist for several decades, and one who does much of his interaction through typing, I expected the on-screen typing experience would be underwhelming. Even with an external wireless keyboard, it still was. And by the time one has the external wireless, and the trackpad, and power supplies for each, or batteries, one is back to in both size and price a MacBook Air. (I choose to use a MacBookPro Retina, which has more resolution, and ports for Thunderbolt, USB 3, flash cards, etc.)
Nonetheless, I expected the iPad to be a big success. A bunch of us were having an evening seminar in downtown Mountain View at a cafe and a lot of students were using Dells and MacBooks. One guy was very skeptical about the just-announced iPad. I predicted that within a year half the tables would be filled with iPads. Turns out I was wrong: less than a year later the 50% point was reached.
(I think tablet percentage is declining because Apple pulled a lot of iPad and iPhone users into getting actual laptops. I now see more Mac laptops than even back then. Probably most of these Mac users also have iPhones, and many have iPads and other such laptops still in their possession.)
Also, many tablets are in vertical application uses, at hospitals, mobile repair services, warehouse inventory, police services, and so on. Doctors and nurses are clearly more likely users of tablets than of either difficult-to-hold laptops or too-small cellphones for professional use.
Does this imply that I think tablets are a growth area? Of course not. Most tablet users have little reason to upgrade. Personally, I stopped following iPad developments several years ago. My first-generation iPad Retina does all I need it to do. I expect this is common.
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