Leaving aside their usefulness as sound and cold insulation (I live in a terraced house!), I think that the whole having/ not having books thing is generation, cultural, and personal.
I have a lot of books. So many I am laughing at those of you on this thread who think YOU do.
But -- I'm an immigrant, spent my late childhood/teen years constantly moving about, then as an adult lived on three different continents owing to work (mine or DH's). I've had to move through various languages and stages of life too. What's I've learned are these points:
-- even in London, it's hard and expensive to get hold of certain books in some of my languages
-- in some countries (eg, I hope not too revealingly, I may point out Sweden) people are more in the habit of having lots of books than in others (eg UK, US: possibly for reason of language availability)
-- while moving around a lot makes moving books a pain (certainly I cull every time), it also makes it psychologically more necessary to have some things that make you feel grounded, weighed down (plus the mover's weight/cost of one single bed is as nothing to so many books)
-- we all have different feelings about this. Eventually, years after marrying my very British husband, I realised that my m-in-law was made nervous by the number of books in our house: to her, they felt like she was in school in an exam. To me, they felt cozy, like my walls were lined with the faces of friends. She and I both read a lot, but we feel differently about having the books around.
-- I guess if I think people lightweight readers it's mostly if they have too many nonfiction books and not enough "real" books. Fiction can be Dickens or a thriller (and Dickens was the thriller writer of his day), but nonfiction is not only NOT more important than fiction, it's usually just an extended magazine article, with facts easily googled and just as quickly forgotten; while in a crisis, whether pandemic or other, the comfort of a beloved, much-re-read, easily-re-read novel or trustworthy mystery novelist is not to be sniffed at
I use my Kindle and I also use physical books heavily. (Library not so much our local council is not good on libraries). Really key books I have on Kindle and in physical copy, sometimes multiple physical copies: the one with my notes in it that my ageing eyes find easier; the one easier to carry in my handbag on the Tube. I have had books in Kindle taken back by Amazon without refund and without notification (1984 and Animal Farm, eg?) and I get rid of 2/3 of the books I buy after reading, as I conclude I'm not that likely to reread them; but I reread a lot.
-- Reference and cookery books as some of you cite? Facts and information can be found online or copied in one page to a binder; Jane Austen or your childhood favourites you can always replace in any second-hand-bookshop (depending on how often you MUST reread them, and if you need them in the middle of the night or the middle of a pandemic), but if you do reread them often, I at least keep them till the next time I move. Art books can be replaced by Pinterest and the internet in general. But a novel that isn't so common, or one that you reread at least once a year, is worth keeping in hard copy.
-- Plus, did I say? They're great for insulating against sound and cold. And if I didn't have mine, I'd probably have a lot of rubbish clutter around to cosy things up, like (cough, cough) pot plants or tchotchkes...