In sum, the author proclaims that without human death, nothing people do has a time limit so people wouldn't have any incentive to do.

But this is false - even if we were a sovereign observer only, the universe is constantly changing and evolving, species go extinct, the seasons are never the same. And we are not just observers, we are also actors - we have opportunities to create today which will not be available in the future. You cannot create the Internet today, it already happened. You cannot spend arbitrary time traveling to and fro across the galaxy to talk to friends, the molten iron geyser you wanted to see at Betelgeuse will no longer be running by the time you get there. Perhaps time motivates us, but our death is not the only thing which limits time.