Because I want minimal complexity. (Usually in the tropics, often with rum and a hammock)
Dead tree books' short term failure modes are water and fire, and once failure is confined to emergencies-that-are-already-emergencies they impose no additional cognitive burden.
Also, I suspect the physical friction involved in "swiping away from" paper books helps reset my dopamine baseline / memory, but that's just suspicion from having lived pre-smartphone.
PS: Also, re: environmental impact. eBay and Amazon sell tons of used books. Sure you're shipping them around, but I really buy new these days.