Why can't I have more than one active Scorecard?

Scorecards are a tool that help you define and track strategic objectives for your partnerships, so, having more than one scorecard active at a time, might cause some confusion as to which objectives the partnership should really be focusing in on. 

Alternatively, you can keep more than one Scorecard on Draft state inside your workspaces, and just activate it if you feel the focus should change and you want to track different goals.