OK, let's consider it differently on those grounds. Just because this world is wher things get done doesn't mean anything to someone considering suicide. Calling suicide immoral is an easy way out. It's a kneejerk reaction. Camus, though, shows how it actually assigns a lot of hope and purpose to life, but a lost opportunity for it.
Suicide is much more complicated than simply immoral.
That denegrates the act to an act of evil, but it is more an act of despair. Calling suicide immoral assumes a morality, a specific path and way of living, and Camus is trying to tell us that it's exactly that kind of thinking that allows for suicide to happen.