Thanos beat him with his fist and the list probably goes on. Imagine Hulk being beat with nothing but a “fist”. This is surprising and I feel Hulk should be able to take more than that before he is defeated.
I was surprised by this as well. It was meant to show how powerful Thanos is I'm sure, but Hulk should've been able to hold his own better without having the Infinity Stones used against him. Made him look weak in comparison to Thanos, which I guess was the point.