That's the difference between a physical and digital product. Physical products have the first sale doctrine and eBooks don't. They are also physically limited. One at a time. Degradation. Shipping. Loss. Theft.

With regard to libraries and eBooks there are two common licenses. One, libraries can loan one copy of one book out at a time n number of times, then they can rebuy it. Similar to a physical book that degrades due to wear. Two, libraries can loan n number of copies of a book out for a fixed per-loan fee.