I never understood why all you folk want to PAY Display prices for onscreen Margins

A 6" kindle has the WIDER display than a (1990's USA) paperback uses for PRINT.
The screen is SHORTER than that same
standard page.
Note: I use the tweak/hack (also available from Calibre via the Kindle Collections PI) to reduce the side margins value from 40 to 10 (= 5 per side)
The text matches pretty much line for line (+/-font face variations)
a Plastic bezel is a lot cheaper than paying for a e-ink display of a larger size, JUST to display... Nothing
So, why must there be full sized e-Ink (side) margins??