No, they wouldn't shut them down. They'd open up the toolbox of administrative law to bleed them. We don't need to pass new laws. (that's what the line about "enforcement" means.) The US Government can just barrage each noncompliant company with investigations, subpoenas, law suits, enforcement actions, national security letters, consent decrees and the like. They can find every issue or abuse of the platforms that no sane person would prosecute, then prosecute (or settle) them. They can sniff out (or manufacture) contradictions in depositions and pin charges of perjury, obstruction, or lying to law enforcement on individuals at the company. Given enough time, a concerted government effort to make life miserable for any of these companies would sap them of money, power, morale, and attention. (Their attention being valuable, the thing that keeps them competitive in the global marketplace.) This is a mirror image of the no-encryption-without-permission issue: administrative law allows the government to punish using process. You can't really run a company of any size except at the government's pleasure, because they can use administrative law to impose arduous costs and punishment through process.

As the other poster has mentioned, they would bleed them.

Yahoo $250,000 daily fine over NSA data refusal was set to double 'every week' https://www.theguardian.com/world/2014/sep/11/yahoo-nsa-laws...

Can you say more about why you think voluntary compliance won't work? AFAIK, all of the companies you've mentioned have had, and continue to have, a mutually beneficial relationship w/ what most people consider to be the U.S. gov't. In what scenario(s) do you envision them (and countless others) jeopardizing that? Thanks.

re-classify encryption as munitions, as they once did?

threaten to jail actual engineers who do it?

threaten to jail CEOs?

Very few people have won a fight with their state. And the costs are usually very high.