API tokens don't need to expire. But having them expire is a nice security benefit. It means that eventually they will be useless even if they are sitting around on an old laptop that gets thrown away.

For many use cases this works well. For example a client app can easily refresh the token from time-to-time. This can be managed with an access/refresh token system (which has the advantage that the token you are frequently sending over the wire doesn't have refresh capabilities)