Being that Hulk gets stronger when he gets angrier, how was Thanos able to knock Hulk out with such ease and why did Hulk not get more angry and increase his strength when fighting Thanos? From what I can see, Thanos did not use the Power Stone in the Infinity Gauntlet.

So how does Thanos beat hulk with such ease?

Edit: I just want add some of the extreme strength feats Comic Hulk has performed and to show that Hulk is an extremely strong being.

• HELD A PLANET TOGETHER


• TORE THE FABRIC OF REALITY


• DESTROYED AN ASTEROID TWICE THE SIZE OF EARTH


• HELD UP A STAR'S WEIGHT


• WITHSTOOD A HUNDRED TRILLION TON PUNCH


• HELD UP A CELESTIAL

Because Thanos is simply stronger than the Hulk.

That statement is not made without controversy, but according to the film's writers in a MovieWeb article he didn't even need the stones,

Avengers: Infinity War has brought up more than a few debates, but screenwriters Christopher Markus and Stephen McFeely have now revealed that Thanos would've beat the Hulk even if he didn't have the Infinity Gauntlet with the Power Stone, fueling more debate. The opening scene takes place on the Asgardian refugee ship after Thanos and his Black Order have taken it over to locate the Tesseract. In a last ditch effort to defeat Thanos, Loki sends the Hulk into a rage to fight. However, the fight doesn't go in the Hulk's favor.

Stephen McFeely believes that the Mad Titan would've destroyed the Hulk with his own bare hands in Infinity War. This would explain why Ebony Maw allows the fight to continue and makes the scene look like Thanos was just having some fun, like a cat playing with a mouse. Looking back at the scene, Maw and Thanos are pretty calm, even when it appears that the Hulk has the upper hand in the battle.

McFeely had this to say when asked if Thanos could still beat Hulk without help. I think he could. I may be speaking out of turn, but I think Thanos could kick the Hulk's ass without the (Power Stone).

This was to establish that Thanos is not to be trifled with,

However, the opening Infinity War scene wasn't just to show that Thanos could beat the Hulk. Marvel Studios boss Kevin Feige revealed early on that the first 5 minutes of Infinity War would show off the immense power of the Mad Titan and he was not kidding around. McFeely explains.

From an in-universe perspective we also have Korath the Pursuer state in Guardians of the Galaxy that

Thanos is the most powerful being in the universe.

This is when Ronan is about to wield the power stone and Korath is trying to stop him.

You can also find the source interview for the above linked article here.

They appear very evenly matched in terms of raw strength, unfortunately for Hulk, strength wasn't the deciding factor in this fight.

Hulk lays out Thanos initially, and Thanos isn't able to push him off - until he's got something to brace against. In a contest of strength between two opponents of approximately equal strength, the winner is going to be the one with greater momentum or something to brace against.

Thanos uses this momentary advantage to get to his feet and set his stance, after which he controls the fight. The Hulk becomes a glorified punching bag because he fights without technique, and against an opponent like Thanos, that's not going to work.

Hulk consistently wins because he's so ridiculously stronger than most of his opponents that his capacity to absorb damage means he can basically ignore technique with the same freedom that he ignores damage.

Against a disciplined technical fighter in his own weight class? He never stood a chance.

We never see the Hulk build up anger. For all we know he could have just woken up in his bed, realising the ship is under attack, smashing a few of Thanos underlings and then go right at him, just because he was awoken in the middle of a good dream. At the least, we know he typically gets angrier if he's in life-threatening situations himself or if the love of his life is in danger. In the MCU, Black Widow gets closest to that and she's not around, nor do we have an indication that he was in serious danger before being beaten by Thanos.

So in-universe, it is likely he wasn't at his full potential and not very focused. And Thanos is likely at least about the same strength level, with better technique (less emotional fighting style) in that fight. Hulk was probably taken by surprise in how strong his opponent was - and we've seen in Age of Ultron, that surprising him when he's not looking/focused/at full strength is a sneaky way to get him out of the picture for a while.

Hulk wasn't ultimately defeated in the sense of about to die, yet a space ship is also a terrible place for the MCU Hulk to fight in. So far, we have no indication to think that he would survive in space. Even if that were the case, breaking the ship apart would kill the remaining Asgardians. And this would likely happen if he were to fully "hulk out" and have an extensive fight against someone at least equally strong. So, in his "mentally improved" state where he can talk and recognizes "friends" properly, he might also have held back on purpose. In any case it was probably a sane decision to just send him away and not drag out the lost fight.

Out of universe, the movie explicitly doesn't focus on him or his mental state. What mood he is in, what fights he had earlier whether he just transformed, whether he already is in disagreement with Banner or not. It builds the question of why he lost and why he hides inside Banner up as a mystery box for the next movie to open and investigate, while for the time being using him and Thor to establish how powerful Thanos is. Up to this point, those two were the top-contenders for "strongest avenger", so it sends a powerful message if Thanos outright beats both(!) - individually.

Personal side note: I sure hope Hulk can pick up that Gimli-Legolas relationship again, solve his mental issues and "level up" as well, after Thor stepped up his game in Ragnarok and IW.