"The 2021 survey, on the other hand, was well into the pandemic, which we would have thought would increase support for companies that brought people goods (Amazon) and information (Google) during a crisis."

I think it actually worked the other way. A lot of folks had only occasional interactions with these companies before. But during the pandemic they had to use them more, so they had to experience more failures. Since negative experiences tend to dominate in our minds, the overall "trust" decreases.