Yes, that's exactly it. When we were young, books were seen as an investment - people had matching sets of encyclopaedias that cost a fortune, and they were the equivalent of investing in a PC 'for the children's education' in the 90s. The marketing surrounded the narrative that they were expensive, but worth it as an investment in the future.
Getting rid of them goes against all of that, and feels 'wrong' to those of us who were part of that way of looking at them.
Just like the computers that had 1 Gig of RAM and needed a separate room, the books went out of date, despite the promises of investment, though. Some subjects are more susceptible to change than others, but few have had knowledge stand still.
Also, there is something about a shelf of books, particularly those in matching sets, that appeals to people - probably more in the case of our generations than subsequent ones. My children use Kindles and Google, and have far fewer books than we do, even though they grew up surrounded by them. When the time comes for them to 'sort out' our things they will see our books as clutter. They may take a couple for sentimental reasons, but most will go to any charity shops that will take them, or into a skip with the rest of our things.