You're not thinking of the typical consumer, who won't have a clue about why using a proprietary service could be bad until the shit hits the fan.
It's all well and good for you - someone who's aware of the risks and issues - to say "just don't use Google/Facebook", but laws would protect the average person who just wants the quickest/easiest way to get an email account or to sign in to websites.
Also even if consumers were all highly educated in the pitfalls of Google etc., major websites still force you to use Google technologies whether you like it or not. Google Recaptcha is everywhere; eBay forces you to use it to sign in to your account. Are people now supposed "just don't use eBay" now as well?