I would ask respectfully, "but then why don't people just send themselves to heaven earlier?"
@Blondie
Because you wont have a physical body in heaven until the resurrection (at the Rapture). Members of God's family who die will be disembodied spirits/souls, awating the resurrection of the body. Being in the presence of the almighty and previously deceased loved ones in a place of pure love and peace is a wonderful alternative to separation from God and all good things he made. But, people would nonetheless like to get back into their bodies as soon as possible.
Phil. 3: 21 - Who will transform our lowly body to be like his glorious body, by the power that enables him even to subject all things to himself.
Also, some people don't think that their work here on earth is done yet. Perhaps they have children they are still mentoring and helping.