Just because we were able to lay out the basic beats of time travel in Avengers: Endgame doesn’t mean that we don’t have any questions about it.
As stated earlier, time travel is always going to come with issues no matter what story it’s being used in.
And even if Steve did place it back there (imagine the awkwardness of him running into Red Skull), does that mean that Black Widow’s death was also undone?
For instance, Red Skull said the price for obtaining the Soul Stone was “everlasting,” so is it even possible to return it to Vormir after it’s been used?