This unfortunately isn't up to them, its the publishers that are enforcing this arbitrary restriction. In fact, IA landed in some preeeety hot water recently for fudging the rules on this very thing [0]. If the IA could get away with handling out an infinite amount of e-books I'm sure they absolutely would.

[0] https://www.npr.org/2023/03/26/1166101459/internet-archive-l...