Libraries are non profits, everyone who works there just gets paid a wage, no one makes more money if libraries make more money.

Or from a systemic standpoint, the library system is effectively separate from the capitalist system we use for distributing everything else. In capitalism if you have no competition you raise prices so you get richer, so functioning capitalism requires multiple copies of everything and a lot of redundancy all actively competing. The library being non-profit sidesteps that effect.