It's a simplified model that assumes a lot. It assumes people know when they're going to die. This is of course not true. It assumes people won't take their keys with them.

But it assumes higher time preference than some people have. Maybe it's your desire to build a nice life for yourself. That's definitely most people. I personally am building a family, and that family has an open ended lifespan if I do it right. What resources I accrue are for mostly after I'm gone. I don't intend to blow it all after retirement on a sports car and a boat.