It's not "theory", it's publicly known facts that companies participating in mass surveillance denied it, and US official lied under oath to Congress (and weren't punished for it) to conceal it. There's no "theory" here.
> You offer no evidence for this incredible assertion.
The evidence to the above is publicly available and has been discussed to death. If you somehow managed to miss all of it, start with https://en.wikipedia.org/wiki/Mass_surveillance_in_the_Unite... and go on the links from there, it will take you some time.
> Some companies have previously collaborated with the government, generally without explicitly lying,
Yes, saying "we do not conduct this particular kind of surveillance ordered by this particular person" while knowing they conduct a slightly different kind of surveillance, ordered by different set of persons - is not explicitly lying. Just like saying "we don't have surveillance technology installed by FBI" if it's installed by NSA instead. There are many ways of lying without "explicitly lying".
> but we cannot jump to the conclusion that all companies would voluntarily lie in a coverup conspiracy
We can not and we do not. We do not know whether any specific company would lie - we just know this option is now very much on the table.
> which, by the way, opens them up to investor lawsuits and risks destroying their branding, for no good reason.
Being on good terms with somebody as powerful as US federal government is a very, very good reason. And I don't see anybody's branding being destroyed so far by the revelation of mass surveillance. We know about https://en.wikipedia.org/wiki/Room_641A and https://en.wikipedia.org/wiki/Hemisphere_Project - has AT&T brand been destroyed? Not in the least. And the government granted them immunity from lawsuits related to this.