My wife worked for a company that specialized in rebinding paperbacks for schools and libraries. It makes more economic sense to do that for niche use cases rather than make all print runs more expensive.
Yeah it depends on the library and collection. If it’s a general-purpose library, probably a pretty limited portion of the collection. If it’s a grad school library with a low-turnover collection, like the one I worked in, that’s totally different. The college I worked for had dozens of libraries and their use cases were all pretty different.