I hear that all the time, but I don’t see how it’s true. Have you priced RDS vs. an EC2? It isn’t even close. You’re paying for the convenience. Not to mention the massive speed loss you take with the increased latency of EBS.
For them, managed DBMS was a life-changing event. As soon as they had RDS or even Azure SQL MI, they were begging the cloud team for more, so they could get their team back.
In some businesses, it's definitely not a big loss to lose agility by having a large portion of your team tangled up in infrastructure management, but for some businesses, that constraint is an impediment to their line of business. Some businesses are missing opportunities for want of infrastructure being able to move fast enough.
Extended support costs on old hardware and software are sometimes astronomical. Then you're paying all of that to get something that, compared to modern gear, performs like ass and just breaks all the time.
I've also had C-suites tell me I have two months to start a project and have all the gear live, but I find we are only allowed to order direct from the manufacturer, and our orders will take 90 days to get to our door. Oh boy. That scenario is difficult to put into terms of money. Sometimes having that one-hop instant supply chain into a cloud service is a huge business enabler, sometimes it's not.