I figured out that there are three reasons why we die:

• We have to make room for the younger generation, so that they can take over, and try and clean up the mess that we left behind.
• We have to call it a day, atone for all our mistakes and come back later in order to keep improving ourselves.
• We have to make haste because there is an inevitable end coming soon, meaning that we are challenged to do as much as possible before it's too late.

Actually, when I think about it more closely, there's one more good reason, namely:

• We have to be thankful and appreciate as much as possible during the finite time that we can live in this wonderful paradise.