The same reason people trust the Dollar as a reserve currency. Yeah, it sucks, but better than any of the alternatives.
Fortunately, there exist open-source/public-domain alternatives for security products. (Doesn't mean that contributors can't be coerced with the equivalent of a Nation Security Letter, though.)
How long until we find out that the "humanitarian aide" so heavily pushed WRT Syria, is an IMF debt loan requiring a central bank and fealty to the US dollar is the primary reason for the opportunity war being sought.
I was talking to a potential client 2 days ago, they provide SaaS to a number of clients, and up until now this has always included data storage.
One of the projects we discussed involved, for a specific customer, moving data storage off the current (US based) server and onto their customer's servers in their own country.
Anecdotal, but still I am really small fish on the far edge of the world, I cannot imagine the reaction where the bigger fish are swimming.
The difference between 'suspected that our confidential data may be compromised by a third party if you believe all the conspiracy theories' and 'know absolutely that our confidential data is being compromised by a third party as we speak' turns out to be pretty big, and worth a lot to international companies who value the commercial value of their private data.