An "order of magnitude superior" is generally the minimum that causes me to start expending engineering effort to move from something implemented and nominally working to something unfamiliar and unimplemented.
10% savings is almost never worth engineering effort. Those engineers are probably worth more than 10% by implementing features or fixing a bug for a customer.
However, even if 10% savings is $1 million, the edge odds probably still aren't in your favor. You may burn engineering time and the project fails or takes 3 times as long. Those engineers are effectively "dead" during that time and whatever contribution they could have made elsewhere is lost. For some reason, nobody ever factors that into their "savings projections".
Obviously, if I've reached the point that 10% savings is $10 million, I'm in a different bucket. But having $100 million in cloud spend probably indicates a lot more problems than AWS vs GCP.
Most businesses like to keep as much of their money as they can. They can use it to pay people and stuff.