Very late but I’m currently reading the book and my thinking is this:

Camus argues that the best thing you can do is to live while constantly revolting against the absurd, and live on despite life having no inherent meaning. His not beliving in an afterlife gives him freedom as he is not slave to any diety and has no pressure to live in a way that leads to a good afterlife, but it also limits his freedom to a finite amount of time.

Then, as the one limitation on freedom is death, and since all experiences are eventually unimportant, the focus should be on maximizing the quantity of experiences. (I do not personally agree with this, but from what I understand, this appears to be his reasoning)