They are big, and bulky. They don't fit into a backpack. And you can't simply hold them in one hand and read, anywhere you sit. Like a bench in a garden. You need a space dedicated to reading them.
In terms of utility, hardcovers are strictly worse.
https://www.amazon.com/Hobbit-Lord-Rings-Deluxe-Pocket/dp/05...
The only hard bound books I’ve ever purchased that wouldn’t fit in a backpack were intentionally oversized “coffee table” books.
I can think of one time in my adult life that my backpack has been anywhere close to that full, which was a weekend trip to New York City where I was testing whether I could get away with not needing to navigate the transit system with a large bag (it worked but didn't really feel worth the effort). A hardcover would be no issue to fit in any normal situation.
That said, when I travel I carry an e-reader and usually pick up a car magazine at the airport newsstand. My physical books stay at home.
“Can’t fit a hardback book into a backpack” is nonsense. Even in middle school and high school hardback books are often exactly what is filling the backpack so full.
But when I pick up a random sci-fi/fantasy book for my own entertainment, I guarantee that taking notes is not a normal use case. Carrying it in my jacket, and reading it wherever I happen to be sitting down, is.
I'm not saying you have to like hardcovers, but I don't find your reasons persuasive TBH.
Sure - if I have a nice chair to sit on in the evening, with good lighting, and can rest it on something, they're quite nice. But the bulk of my reading is either outside of home (so they need to fit in my bag nicely) in an uncomfortable chair, or while lying down so I need to hold the book up. Weight/size really matters here.
When I was a kid I asked around, and in those days the reasons I was given were:
1. They're durable - less likely to fall apart - and may last generations.
2. The font is bigger.
Having the survivors of the Great Depression around was amazing as far as mindsets go. I miss those folks.