As a Google customer (of both Compute/Container Engine and Cloud SQL), I'd rather use a Mysql instance hosted next to my application on Google's network than a Postgres instance that's an internet-hop away in Amazon's cloud. If I was currently running my apps on AWS that's where my DB would live too (and I'd be using RDS Posgres there).

The other reasons listed are an order of magnitude less important for my cost/benefit calculus (though things like cost and support will definitely matter to orgs bigger than mine).