Why The Time-Keepers Didn't Intervene In Avengers: Endgame
Loki will introduce the MCU's Time-Keepers - and here's why this mysterious group didn't get involved in the events of Avengers: Endgame. The MCU introduced the idea of manipulating time in 2016's Doctor Strange, but it wasn't until 2019's Avengers: Endgame that time travel itself became an important part of the franchise. That blockbuster film saw the Avengers use time travel to collect the Infinity Stones from points prior to their destruction; they then returned to their own time and used these to restore the untold billions of lives Thanos had extinguished. The precise mechanics were unclear - Endgame's writers and directors disagree over the rules of time travel in the MCU - but, in truth, all that matters is that the Avengers' ploy worked.
Loki will continue to develop the theme of time travel in the MCU. The show stars a version (or "variant") of Tom Hiddleston's Loki from a branched timeline inadvertently created by the Avengers, and it seems he will fall foul of a group informally known as the Time-Keepers. The Temporal Variance Authority (or TVA for short) believe they are responsible for protecting the integrity of the timeline, and Loki's prior knowledge of them raises the possibility they have crossed the path of Asgardians before. But why didn't the Time-Keepers get involved in Avengers: Endgame?
The group of Avengers who traveled back to 2012 initially intended to take the Infinity Stones, with no real understanding of the consequences to the timeline. Fortunately the Hulk confronted the Ancient One, a powerful sorceress who had intimate knowledge of temporal mechanics due to her centuries wielding the Time Stone. She revealed the removal of the Infinity Stones from their proper places in the timeline would create branches in reality; crucially, she also told the Avengers that returning the Infinity Stones would seal these branches off, maintaining the integrity of the proper timeline.
The Ancient One claimed branches were only created by interfering with the Infinity Stones, which she said maintain "the flow of time" in the universe; but an organization like the Time-Keepers wouldn't be needed to monitor the timeline if that were the case, because branches would only be created in unique circumstances where time travel interacted with an Infinity Stone. It's reasonable to assume the Ancient One was oversimplifying, but what really matters is that she was telling the Avengers how to ensure they didn't cause lasting damage to the timeline. Consequently, the Time-Keepers wouldn't have needed to interfere in the Avengers' actions, because they knew things would be put right in the end.
This does raise an intriguing question, however; is there a loose relationship between the Time-Keepers and the Masters of the Mystic Arts? They would presumably be particularly interested in monitoring the Time Stone, which would have been a source of countless temporal anomalies as different sorcerers experimented with it over the generations. The Book of Cagliostro recounted the risks of using the Time Stone, with Wong and Mordo cautioning Doctor Strange that he could unwittingly "create branches in time. Unstable dimensional openings. Spatial paradoxes. Time loops!" Presumably the sorcerers learned the hard way, and it's quite possible the Time-Keepers helped them sort out the various messes they had made. The Ancient One, as likely the longest-lasting bearer of the Time Stone, may well have wound up working alongside the Time-Keepers on occasion. The story potential of Loki's Time-Keepers is absolutely tremendous.