Thor's goal at that moment wasn't saving the day, it wasn't stopping Thanos, it was revenge, pure and simple. He wanted to punish Thanos for killing so many of his people, and we know from Endgame that his own issues may have been projected onto the Titan.
Iron Man Made the Ultimate Sacrifice to Defeat Thanos
During Endgame, The Avengers traveled through time to acquire the six Infinity Stones and snap back everyone originally blipped in Infinity War using Tony Stark's Nano Gauntlet.
However, Ultron, who was fascinated with the Stones, effortlessly killed Thanos by cutting his body in half with a laser beam from the Mind Stone and obtained all the Stones for himself which turned him into a cosmic being.
AVENGERS: ENDGAME Clip - "I Went For The Head" (2019) Marvel
Could vision actually cut Thanos in half?
How hungry for power was Ultron that he was able to literally slice Thanos in half with the Mind Stone? Why couldn't Vision do that? Because Ultron is using the Stone's full potential compared to Vision who barely knows how to use it at all.
Mjølnir: Thor was wielding the magical Uru hammer, which he had lost when he was banished from Asgard. However, before Thor could retrieve the Mjølnir from S.H.I.E.L.D., he was killed by Hawkeye.
Before he could say anything else, an enraged Thor decapitated Thanos, killing the Mad Titan. When Rocket asked what he had done, Thor replied that this time, he went for the head.
Thanos and Hulk have clashed several times in Marvel lore, with Thanos even admitting he was scared to face the Hulk before acquiring the Infinity Stones. While Thanos is usually the victor, it's generally down to him using superior tactics and technology, rather than simply possessing greater physical strength.
Yes Loki is dead, he got killed by Thanos in Avengers Infinity War (2018). But the Loki from the Loki series, is indeed Loki, but not the same Loki that died in Infinity War.
Who would win in an MCU fight: Odin or Thanos? Without the Infinity Gauntlet, Thanos stands little chance against Prime Odin. Odin is stated to be able to shatter the Earth.
Thanos only hijacked Thor's ship, murdered his brother with his bare hands, stabbed his best friend through the aorta, slaughtered half of what remained of his people, left him floating in the middle of space like a discharge from the sewage tank, and then proceeded to obliterate half the universe on what Thor ...
Indeed, during the time heist, 2014 Thanos witnesses the death of his 2019 self and proclaims, “And that is destiny”, choosing to embrace this vision when 2014 Thanos travels into 2019, where his last words are: “I am inevitable.” In some ways, Thanos dies what we might call a very good death.
While Thanos didn't specifically try to kill the God of Thunder, he and the Black Order detonated the Asgardian refugee ship after he acquired the Space Stone from Loki. So perhaps he assumed that Thor was effectively killed in the blast.
Dying in his brother's arms, Loki answers Thor's, “I'll tell father what you did here today,” with these bittersweet words. Both are referencing a line from the first Thor film when Loki is falling off the Bifrost and shouts to Odin, “I could have done it, Father!
The God of Thunder let himself go, but not just in the sense that he'd done little more for five years than chug beer and play video games. Thor's spirit was broken, his purpose lost, and his ability to simply accept himself and his actions crippled, by Thanos' victory.
This is shown later in the series, where heroes acting on a precognitive vision of a rampaging Hulk, Bruce was then shot in the hypothalamus by Hawkeye who was hiding on a tree nearby.
In the 2019 film Avengers: Endgame, Iron Man (Robert Downey, Jr.) steals the infinity stones from Thanos and transfers them to his own suit. When Iron Man snaps, he gets rid of Thanos's army, but this action kills him.
By far the most brutal death is when Deadpool kills Spider-Man while wearing the Venom symbiote. Deadpool uses the symbiote's ability to bypass Peter's spider-sense in order to ambush him. He then quickly overpowers Spider-Man, and horrifyingly, eats his brain while Peter is completely helpless to stop him.
He simply wanted him dead at all costs because he was his biggest threat. As per the user, the director of Avengers confirmed that Thanos was most scared of Iron Man. “Not because of his strength, not because of his power, not because of his power, but because of his suit,” he added.
Ultimately, the Avengers thwart him once more while Wanda and the Vision destroy Ultron's body and Ultron himself respectively. An alternate timeline variant of Ultron appears in the Disney+ animated series What If...? (2021), voiced by Ross Marquand.
With what seemed to be his last bit of strength, Thanos, much to Thor's horror, snapped his fingers to activate the Infinity Gauntlet and passed out. He awakened in the Soulworld where he found a younger Gamora, who asked him if he completed his mission. He solemnly replied he had.
