No idea what their expectations were, but not surprising to me. The average joe Gamer isn't that fussed about graphics and is more likely to stick with their regular PS4, while average Joes that hadn't bought in yet where more likely to bet swayed by one of the super cheap slim bundles. A lot, at least of those remotely aware of what it is, probably think it's only worth it with a 4K TV they don't have/plan to buy soon as well.
I love mine, and I'm glad I upgraded, but it always seemed clear that these mid gen upgrades would be for enthusiasts while the cheaper Slim bundles still sold a lot more. It will be interesting to see how Scorpio does as it's later in the gen, an update to a console that's sold a lot less units, and more of a power boost (though maybe at a higher price as well).