A number of reasons. To further make dying an actual penalty. To discourage people repeatedly respawning to get FS. And, in anticipation of combat, so that you can't die and then respawn to join the same battle you were killed in.
"May the Grace of Ara go with you, and His Vengeance be wrought upon your enemies."
Well the original question has only slightly been answered. Im curious why it is specifically 21 days, 3 weeks? And not 2 weeks, or 4? or 25 days, or any other combination of numbers?
Was there any specific reason that 21 was decided as the magic number?
Not that Im complaining, Im actually merely curious.
It actually used to be three months, because that was deemed a sufficient penalty. However, at the time that number was chosen, dying was not possible at all yet. Sometime between then and now, when the prospect of dying was actually starting to become relevant, a couple staff and helpers got together to form a temporary death rules team and spent some time discussing the new length. It was generally agreed that the duration needed to be reduced, and three weeks was chosen as a reasonable period of time through the process of negotiating between people who wanted it longer and people who wanted it shorter. :p