By analogy, Google Docs isn't marketed for healthcare use. If you wanted, you could put a bunch of PHI in a Google doc and it wouldn't be their responsibility. They certainly didn't tell you to do that. However, if they marketed Google Docs as a great place to store PHI, yeah, then suddenly they're on the hook for complying with the relevant laws like HIPAA.
(Although in this case Google will sign a HIPAA business associate agreement with you and voluntarily agree to comply. They still don't market it that way, or at least don't predominantly do so.)