That's an incredibly naive assessment and is absolutely not true in practice, except for perhaps for some orgs where the stars just happen to align to make that a reality. Most places heavily build "cloud" into their frameworks, tooling, hiring, and, well, everything. Even just swapping out a single hosted/managed component (as my company did a few years ago, replacing Kinesis with Kafka) can require a lot of up-front work[0] and on-going maintenance.
[0] Especially if you're already in production with the thing you want to replace, and want to transition without downtime for your customers.
I love that you think mature products that took teams of highly skilled people at Amazon years to refine can just be slapped together in a month in your colo.
