You cut the first piece, realize you actually need a different type of saw for the next cut, it's booked out, now your project is indefinitely delayed.
They are similar because in both cases you are sacrificing resiliency (multiple copies of a resource), for efficiency (a singular shared copy).
A tool library is still a great idea / resource for when you're doing a project and need one weird tool that youll never use again, but most people who do any real amount of DIY over their lives will want their own set of tools that cover most of the bases.