Why doesn't Thanos kill Thor?
The beginning of the movie focuses on Thanos obtaining the Space Stone from Loki, who he kills for attempting to kill him while Loki pretended to offer his allegiance and guidance on Earth. After killing everyone aboard the ship, which includes killing both Loki and Heimdall, Thanos and his Black Order departed the vessel, leaving Thor alive. Why?
Towards the end of the film, Thanos is seen about to kill Tony for trying to stop him, but he doesn't choose to kill Thor for the same reason. And it seems that the only reason Heimdall dies is because he transported Hulk back to Earth through the Bifrost (as mentioned). Thor is arguably Thanos' greatest enemy (as evidenced towards the end of the movie), and they had him secured. It just seems strange - Thanos decides to destroy the ship using the Power Stone but not kill the last person remaining on it. That could've been because they wanted Thor to suffer, but audiences probably will never know.
How does Heimdall know to send Hulk to Doctor Strange?
It was revealed fairly early on that Hulk arrives in the Sanctum Sanctorum and warns everyone about Thanos - it was even shown in the film's trailers and clips - but how he got there was always a mystery going into the movie. It becomes clear that Heimdall actually sends Hulk to Earth when Thanos and the Black Order are a bit distracted. But how does Heimdall know to do that?
Thor is captured at that moment, and he doesn't tell Heimdall to do that, nor does he tell him to send Hulk to the Sanctum Sanctorum. What's interesting is that omni-senses are one of Heimdall's many powers, meaning he can see pretty much every soul in the universe. He used that multiple times throughout the franchise, which is why it's possible that Heimdall could sense that Thor wanted Hulk sent to Earth, but that's still a reach without any sort of confirmation.
Why doesn't Heimdall Bifrost everyone out (or Thanos)?
What's interesting about Heimdall sending Hulk to Earth is that he mumbles in incantation requesting his forefathers to let dark magic flow through him once more, which then opens up the Bifrost allowing him to send Hulk away. How he knew to send him to Doctor Strange, though, and how he did so remains unclear. If Heimdall can summon the Bifrost from somewhere other than Asgard, then why hasn't he done it before and why didn't they all escape together? The Bifrost can certainly transport multiple people at a time to different realms.
Granted, the only other time something like that has happened was when Thor came to Earth in the first Avengers movie, which was chalked up to Odin summoning dark magic. Taking that into account, it's possible only one person can be transported at a time. But again, that's just a potential answer to a question that has been asked multiple times since 2012 - and it doesn't seem like it's going to go away anytime soon.
- Avengers: Infinity War / The Avengers 3 (2018) release date: Apr 27, 2018
- The Avengers 4 / Avengers: Endgame (2019) release date: Apr 26, 2019
- Spider-Man: Far From Home (2019) release date: Jul 02, 2019
- Captain Marvel (2019) release date: Mar 08, 2019
- Ant-Man & The Wasp (2018) release date: Jul 06, 2018