Earlier quoted context omitted.
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…
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.