It's nowhere near enough notice to take reasonable action.
You say it could be done in a weekend. Do you know this because you've done it?
To do anything other than an emergency exit, you need time to evaluate and select alternatives, and that doesn't include things like GMail, where there needs to be an overlap for people to update my address etc. (yes I used my own domain - no google didn't make it transparent enough that my gmail address didn't leak out).
As for the flood zone analogy - that's absurd. At some point along the way I'd have had to decide I was going to stop using them. In my case that point is now.
You seem to be suggesting that it should have been before now, and that a change in terms and conditions isn't a reasonable indication of their future direction.
Consider that Google's could have changed their T&Cs in the other direction - to commit to greater segregation of user data had they thought this was important.
They didn't.