You. Would. Have. To. Pay. The. Same. Even. If. It. Didn't. Come. With. A. PDF.
Why do people not understand that?
People do understand that, and that's what they resent. People have invested a lot of money in the hardback books, more per book than the PDFs cost. They've already given their money to Paizo, and they resent being left out in the cold for it.
I'm fortunate enough to have caught the deal they had on Humble Bundle a while back, and to have taken advantage of some convention deals where I got a PDF code along with a hardback purchase. So most of what I might purchase from the content market (pending my hopeful reinstatement of gainful employment), I already have the PDFs.
But for the people who say they've already invested heavily in the hardbacks, if I were in their shoes, I'd feel slighted by Paizo as well. Some of these people have been Paizo customers since longer than PDFs have been around. Some of these people have been loyal in supporting their local game shop. Paizo still got their fair share, and they're leaving some of their oldest and most loyal customers out in the cold. Some of these people just don't like PDFs.
We can debate reasons and practicalities regarding Paizo's policy, but the bottom line is that people who have already paid them more per book than people who have bought the PDFs are being treated, whether intentional or not, as second-class customers.
And whether you agree with them or not, you can at least try to understand why they feel the way they do. Put your feet in their shoes for a while. Most people have a set income from which rents and mortgages have to paid, children have to be clothed, fed and educated, medical bills have to be paid, and car payments have to be made. Then to be told, "yes, you bought several of our expensive books, and you bought this great program, for which you'll likely keep paying for cloud services, but if you want our product available in this program, you have buy all those books AGAIN. Sorry bout that. Have a nice day."
That pill doesn't go down so easily.