Insistent strategy Every person who designed a spreadsheet that makes up your "system" did so from their individual perspective, view-point and metrics. Each spreadsheet in use, though important pieces of the puzzle, are not interconnected to the logic, algorithms and data of the other spreadsheets. This does not roll up into a choesive strategy dirving the best performace and decision making for the company as a whole.
Communication overload We cannot just do our jobs. We need to spend a lot of time pouring through the details of (or consolidating) spreadsheets as necessary preparation to go back and update our own spreadsheets to do our work.
Only receiving relevant information at update time In many cases, we work with week-old data until a spreadsheet is updated and communicated. A lot changes over the course of a week in most environments
Cost We dont have a budget for advanced forecasting tools though im not convinced that any of thse would solve the problem anyway but what is the cost of all of the time invested in building, maintaining and communicating spreadsheets?