"How is this not obvious to everyone? As we advance it becomes more difficult to advance. "

It's a type of recent change blindness. Because for the last few years there are seemingly impossible breakthroughs every few months. Literally, things everyone said would take 30 or 100 years, happen within months. It is really easy to think this will continue. The new normal. Really, we haven't seen it slow down at all, so why would we expect the miracles to stop all of a sudden?

It seems like accelerating, and decelerating, are both fair game as future directions at this point.

So it is nice that the paper put some weight behind the argument that this could all grind to a halt for a lot of different reasons beyond the hype.