Because all it takes is a list. The company email password is a variation of the ERP one; the ERP one is the same as that of a personal online shop that suffered a data breach two years ago; that list is up for sale. All anyone has to do is try it.
The root of the problem is arithmetic. Each employee handles 30 to 80 credentials: email, management software, supplier portals, online banking, cloud applications, Wi-Fi, printers, the brand’s social networks. Nobody keeps 80 long, distinct passwords in their head, and the improvised solution is always the same, reuse them, write them on a note stuck to the monitor or create a “passwords.xlsx”.