Why Cloud Migrations Fail

In my experience: Failure to get buy-in and include relevant architectural and operational experts in the evaluation and planning processes.

"cloud" it's just a synonym of "someone else computer", what someone do on someone else computer matter. If for cloud we intend VPS, well, I expect next to zero issues, because someone else computer "origin" and "destination" are essentially the same. When cloud means someone else stack on someone else computer, well, that's not standard, so "migration" could means full-rewrite of an infra built on top of the aforementioned someone else stack, to someone other stack, the use of an "equivalent stack translator", let's say a wine (windows api emulator) for cloud etc etc etc.

What managers refuse to learn is simply this "cloud" does not means a specific tech, offered by a handful of vendors.

It is simply a lack of skilled staff. The industry has plenty of mediocre people who struggle to follow a playbook, but hardly any people who can write the playbook. It is a common trope that the government is like this, but over the last 5 years I have observed it to be true at every organisation I've encountered.