Nobody sets out to run a nursery on one shared password. It creeps in. A single account is set up on the shop-floor till "just to get going." A seasonal picker needs to log a count, so someone reads the password out across the bench. A manager leaves, and their login keeps working because changing it would mean telling six people a new one. Convenience wins, one small decision at a time, until the password lives on a sticky note by the screen and everybody knows it.
The cost stays invisible right up until the moment it isn't. A price is changed and no one can say by whom. A batch is written off and the record shows only "the shared user." A worker who left in spring can still reach your customer list in autumn. None of these is a disaster on its own, but each is the kind of gap that turns a routine question into an uncomfortable one.
What helps is a system where the easy way to sign in is also the accountable one: each person is themselves, holds exactly the access their job needs, and can be switched off the day they leave.