Why does everything need a reason? Nobody really knows enough about what could happen on timescales that large. We've invented dark matter to explain the acce

Why does everything need a reason? Nobody really knows enough about what could happen on timescales that large. We've invented dark matter to explain the accelerating expansion of the universe because we don't have any proof of why that is happening. One thing is clear to me though, and that is that both Earth and the universe will outlive me. So no matter what happens to the universe, it's not my problem and I'm back to, "it's my choice whether I just sit here depressed about my imminent demise, or just forget about that which I have no control over and just try to enjoy myself as much as I can".