Was Thanos really waiting for all these characters to die?

Question

There's been a theory floating around the internet that Thanos waited so long to make his move to assemble the Infinity Gauntlet because the most powerful beings in the universe were still alive. The characters I am talking about are Odin, Ego the Living Planet, and the Ancient One. (See, for example, this article on Inverse.com.)

I re-watched Doctor Strange recently, and in that movie, after the Ancient One's death, Baron Mordo states that news of her death would spread throughout the universe.

I personally don't subscribe to the theory that Thanos waited for these people to die (Thor: Ragnarok takes place too close to Avengers: Infinity War for news of Odin's death to spread that quickly), but have the Russo brothers or the screenwriters commented on it? Is there any truth in the internet's words?

Answer 1

Per the film's Directors/Screenwriters Commentary, Thanos' motivation for deciding to gather the stones is that he finally (after many years of searching) learned the location of the lost Soul Stone. Before this he seems content to get on with obliterating one planet at a time and making sure that he knows roughly where the other stones are, safe in the knowledge that he's made himself powerful enough (through his armies and his 'children of Thanos') to go and collect them when the need arises.

Stephen McFeely: "The catalyst for the whole movie was when Thanos figured out where the Soul Stone was because he captured Nebula on his ship and rooted around in her brain and figured out that Gamora knew where the Soul Stone was."

Joseph Russo: "It's the reason why he hasn't gone for it before, because he knows that the minute he does, the forces of the universe are gonna line up against him. If he doesn't know where the Soul Stone is, then what's the point?"

Answer 2

From Inverse.com:

'Avengers: Infinity War' Doesn't Actually Have a Mind Stone "Plot Hole"

Thanos has been culling populations for decades; He kidnapped Gamora around 18 years ago but has had his genocidal tendencies for far longer. He’s quietly sought Infinity Stones for years. He sent Gamora hunting for the Soul Stone long before the first Guardians of the Galaxy. But in Avengers, if Thanos had gotten directly involved and attacked Earth for the Tesseract himself, then he might have attracted the attention of characters like Odin, Ego, or the Ancient One, who could have contested his mission. Manipulating Loki into a red herring was a safer play, especially when Thanos couldn’t fully wield the Stones at that point.

It wasn’t until after Odin died in Thor: Ragnarok that Thanos had the chance to attack Nidavellir and force the dwarf king Eitri (Peter Dinklage) to build the Infinity Gauntlet. We know from a brief exchange between Eitri and Thor that the space station was under the protection of Asgard, so when Odin’s death unleashed Hela, leading to the destruction of Asgard, the dwarves were left unguarded. That’s when Thanos struck, had the Gauntlet made, and then quickly took each Stone one-by-one until he eliminated half the universe.