It's not the only reason, technologies do plateau. We're not living in orbiting cities flying fusion powered vehicles around, even though we built rockets and nuclear power more than half a century ago.
Do you have evidence or empirical arguments to the contrary?
I just find the belief that the continuous rapid improvements in machine intelligence stopping just short of human intelligence quite arbitrary.
It's a view I don't share at all. I don't see anything that could be even remotely considered intelligent under any reasonable definition of the term. Useful in places, yes. Intelligence, hard no. So the question of whether it will approch or surpass human intelligence makes no sense to me, because the technology and its progress are in an entirely different dimension and unrelated to that idea or goal.