I think one of the major contributors that is often not mentioned with cloud providers are the actual setup/human maintenance savings. As is, the premium that is added to the 'managed' services is usually much less than what would cost a DevOps to maintai /run. I.e - it is safe to assume (at least the market that I'm in) that 1 hour of DevOps services will cost 150USD. 10 hours would be 1. 5K USD. That is actually enough to host a PHP based medium sized ecommerce solution by using purely managed services for about a month (<500 orders/day, using AWS ECS, RDS, ALB, OpenSearch, ElastiCache). Sure, there is still the DevOps cost attached to such solutions, but it is drastically lower than on premis. I've been using these arguments with my customers to migrate them to AWS for the past few years (since Fargate wide adoption) and its been great so far. I do not think that saving money should be the primary reason to migrate to the major cloud providers. The primary reasons should be the increased robustness, ease of maintenance and additional tools that you get.

PS. This is written entirely from the perspective of running multiple small/medium ecommerce solutions (500 - 2000 usd/mo AWS bill) using the stack mentioned above. I have no real world experience doing grand scale setups.