12 months notice is too short for big non-tech enterprises. They plan their infrastructure needs in 5-year terms. Changing to a new environment takes re-educating a lot of people, going through a lot of legal and audit meetings, finding enough manpower to do the transfer, putting things on hold purely for the migration,...
12 months is the time for the contracts to settle between these enterprises and cloud-vendors.
If your company is that big and unwieldy that a tiny chance of needing to do a migration in 12 months is unacceptable, you can stick to the key services which offer 36 months of notice. For all I know at that point you can negotiate your own guarantee if you're so big.
If you work at a company that can't do a cloud infra migration in 36 months, I don't have any good advice for you, but I doubt most commenters on here fall into that bucket. Frankly, I would expect companies that large to be in all the clouds so that you could negotiate them against each other, but I doubt that impacts many people here, and the chance of any of these worst case scenarios happening is vanishingly small.
This isn't a tiny change, if GCloud says "we quit in a year". That is a huge change. Applications using GCloud SDK for services suddenly need to be reworked and redrawn. That alone is a huge change for non-tech companies.
Some companies even need to check with the laws they reside in if the new cloud vendor can even be used.
Just work in any financial, medical, pharmaceutical, government-related... company and you'll understand that a year is nothing for these companies.
12 months is the time for the contracts to settle between these enterprises and cloud-vendors.