I guess it's like doing anything (like working at a job, even one we like) for a long time - we don't want to do it forever. After a few decades (if that), we're ready for a change, we want to move on to something else.
If there is a heaven, one would think that getting there would open up incredible vistas that we have trouble conceiving at this time. On the surface, being there forever would appear to be boring. But it's a big universe, and that's just the part we can observe via telescopes.
But it would have to be purposeful. We'd have to be achieving something up there. Otherwise, what good would it be?