Doctor Strange said that he saw 14,000,605 outcomes. It is safe to assume that he saw Thor going for the head. What would be the alternative outcome if he did aim Stormbreaker at Thanos' head?
1 Answer
In none of the other 14,000,604 potential outcomes did Doctor Strange see a positive outcome. That doesn't necessarily mean that Thor can't kill Thanos per se, merely that doing so would lead to another one of the unpleasant outcomes that Strange wanted to avoid (for example, his troops in space taking his death badly and obliterating Earth from orbit or Thanos' death leading to an even bigger threat taking a swing at the Avengers).
This leaves us with two routes, one likely, one implausible.
- Route #1 - In some of the outcomes Thor does indeed kill Thanos by aiming for the head (or cutting off his hand and dispatching him afterwards) but that that subsequently leads to other bad things happening.
or
- Route #2 - Thor doesn't (or can't) hit Thanos in the head in any of the millions of outcomes for some reason.