Atheists work like there's no tomorrow because for them, of course, the understanding is that there is no tomorrow. If time destroys all legacies you'd best work as hard, as long, and as fast as you can to shore up whatever you can, not just for the sake of having what you made last a little bit longer but also because your work is what you have. There is nothing better than to enjoy one's work one finds to do.
All work and all skill in work spring from man's envy of his neighbor per Ecclesiastes 4:4. Ecclesiastes lays out succinctly what can drive an atheist to keep working, but not just an atheist. It's not "just" an atheist who does all his or her work and skill acquisition out of envy of one's neighbor. So it's not a huge surprise atheists have a great incentive to work both for work as a pleasure in itself and as a testament to the work. John Lennon used to say that the goal was to beat Elvis and then after the Beatles bested Elvis in charts a new goal had to be found. For people who are into the Beatles envy is a major reason the Beatles did what they did. Of course it might be useful to distinguish between envy that is purely covetous and an envy that has some genuine admiration in it. But I feel too lazy, heh, to bother with such distinctions in this post. I have places to be.