Who's giving them a choice, other than not buying anything at all?
I think people value the benefits of the non-modular design more than you think.
I think people value other things that may or may not have anything to do with the lack of modularity, and I think they buy devices that have those benefits. Often, they probably don't even realise the lack of modularity or its implications at the time of making a purchasing decision, but even if they did, they might still value the other benefits over any downside due to lack of modularity.
We can't really conclude much from the current trends unless manufacturers also offer devices that have the benefits of modularity as well, potentially at a greater cost literally or in terms of things like bigger size or heavier weight.
No, you wouldn't.
But even leaving aside the obvious hyperbole of your comment, we're drifting away from the topic at hand. My argument is simply that proprietary-everything, all-in-one designs are a significant loss for the consumer and a huge win for the manufacturer, because they very effectively kill both the upgrade and repair industries, making the default response to buy more new equipment instead.
Given the disproportionately high rate of damage to mobile devices, and the relatively low starting specs, and the fact that most laptops (including Apple ones) have not had such severely restricted maintainability until very recently, this all seems like a huge step in the wrong direction, from the customer's point of view.
If it were only the screen on the Retina MBP, I could just about believe the theory that it was done to keep the size down, but it's obviously not only that screen. If you look at the direction of basically all Apple equipment in recent years, not just phones or even laptops, everything has been moving towards using unusual/proprietary connections and fixed-at-birth specifications for a while, and there are far too many cases where there was no apparent benefit of any kind for me to accept that it's all being done because it's what the customer wants. Fool me once, shame on you. Fool me dozens of times over a period of years, find me a good shrink.