The problem isn't "some code which different services use is in a library".
The problem is an not-ideal "the code which is in libraries shared by different services is tightly-coupled to particular services". e.g. changing the shared library might break some service which depends on it.
Obviously, you don't want code like that. But it's easy to write code which is slightly coupled; and then when you're in a hurry, to increase the coupling.