That's not a minor consideration from me as I can easily fill 64--128 GB of total storage (about 30GB seem to be system + apps).
That's not all books --- I keep a fairly large number of podcast episodes downloaded. But at about 5 MB/book, even an apparently generous storage quickly shows limits.
I passed on the ReMarkable as its 16 GB storage (about 8GB available) only permits 1,600 books at 5 MB/book.
(And that's without podcasts or audio.)
The BOOX has a 64 GB onboard storage, maximum. I've got that near capacity in about 6 months, though a large share of that is podcasts. My preference would be 256 GB. Plus far better content-management capabilities on the device itself. I think I could live within that.
Retail cost is $20, falling by about half every 2 years. The minimising of eBook storage makes absolutely no economic sense.
A modest e-book reader runs about $200. That's the cost of about 3 cases of 20# letter-sized paper (10 reams/case), or 15,000 sheets of paper.
At ~300 pages/book, that's about 50 books cost equivalent.
Note that printing output tends to run higher, at $0.01 -- $0.25 per page (higher for colour inkjet and laserjet).
Depending on ones reading patterns, the cost (and environmental impacts) of an ebook reader could well come out ahead. It's also generally easier to carry such a device than the equivalent number of printed books or documents.