Why can't I re-install my license on a machine that I have previously deleted?

There are several reasons why we block the reactivation of a slot deleted by the user, the following example is just one of the many possible cases:

A user sells his old computer leaving all his software installed and activated; later he decides to deactivate the software left on the old computer and reuse his license on his new computer. If we did not give the possibility to deactivate a slot, the owner of the new computer could launch the software and it would reactivate automatically since the license is still installed on that machine. 

Of course, if a user deactivates a slot by mistake and wants to reactivate it, he just needs to contact us and we will satisfy his request, as long as it comes from the legitimate owner of the license.