[uvTwitch]

Because Microsoft and Google are both much, much larger companies that have more than one business avenue, not to mention deeper pockets for lawyers. When asked for a user's data, they are are far more likely to respond with 'fuck off' than a small single-business-model company with a known government war criminal on the board of directors.

[toni]

Microsoft, Google, Facebook and Yahoo have no incentive to show their middle finger to the government.

As soon as your company receive a subpoena (or even a "national security letter" for that matter) from the government to hand over your users' data, the size of your company or your business model does not matter at all.

Don't hold your breath for Microsoft, Yahoo and Google to fight for your rights. The same goes for Dropbox. That is why suggesting to move from Dropbox to Microsoft/Google Drive does not make any sense.