The Time Variance Authority thought Loki was a prisoner but, naturally, it didn't take long for him to escape and go on a jaunt through the TVA's mysterious city. But the trickster god was stunned into silence when he saw a drawer full of different versions of the Infinity Stones - Time Stones, Space Stones, Reality Stones, and even one of the most-coveted Soul Stones. It makes sense that objects of great power or great value would be the cause of branches in the timeline, because they would tempt people to do something they weren't supposed to. Loki was finally broken at the sight of the Infinity Stones, shaken at the idea the objects that had dictated his entire life amounted to junk discarded in a TVA drawer of evidence. But why are these Infinity Stones powerless in the city?

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The MCU's Infinity Stones are, of course, based on the Infinity Gems seen in the comics. These have never been treated in an entirely consistent manner, largely because numerous writers have handled the Infinity Gems over the decades, and there have been numerous retcons and rewrites. Still, the comics of the last decade or so have stressed that an Infinity Gem can only work in the universe it originated from. When someone travels outside that universe, say by jumping to a parallel dimension, the Infinity Gems become powerless. That was actually a major plot point during Jonathan Hickman's New Avengers run, which served as a major source of inspiration for the Infinity Saga - even introducing Thanos' servants the Black Order.

Dialogue in Miss Minutes in Loki's TVA briefing - and she revealed the Infinity Stones "create what you experience as the flow of time." In other words, the Infinity Stones are bound to the nature of reality itself in their home dimension, and if removed it wouldn't be a surprise to find they lose their power.