Generally it's because nothing is documented. All the knowledge about a system is in the previous employee's head. Now it all has to be pieced together from wh

Generally it's because nothing is documented. All the knowledge about a system is in the previous employee's head. Now it all has to be pieced together from what code and configuration exists. Nobody documented the shortcuts, the rationale for why it is coded/configured that way, or the quirks or bugs in the system. Of course none of this can be put into a spreadsheet thus it doesn't exist, as far as management is concerned.