Well, that's kinda the point.

If you assume that all we get is what we have while we're alive, then that life becomes the point

A lot of people that reach the conclusions you have, opt out. They move into a commune, they go vagabond, they may choose to just flit between jobs and find whatever fun is in them.

Or, they may decide to become focused on finding purpose within the world that is, the societal structures as they exist. Some of those devote themselves to service, or find jobs that they believe make life better for others.

Some stay in the framework of things, but do the bare minimum and focus on their off time their purpose.

The point of it, from that point of view where this is all we get, is to find what makes staying alive worth it.

It isn't like the certainty of no afterlife removes your ability to live and love and do good things. It can make it harder to bear the bad things of life as well, but that's anything really.

The point is what you decide it is.