1. I know the risk of only being able to peer through the fence at the distant piece of software that is running your business, unable to gain any insight while your production application is limping badly and customers are running away like water. On top of that, thrashing it out with Mr Clippy is better than average support. If my business depends on it I want experts at hand who have the tools and the access they need to do the job they do.
2. The insane pace of serverless is entirely fad driven and lacks quality engineering which is required for critical pieces of software. The tools are universally poor quality, unstable, unreliable, poorly documented and built on gaining mindshare, making IPO and selling conference seats. Best practice never materialise as the rate of change does not allow an ecosystem to settle and work the bugs out. The friction is absolutely terrible but no one speaks of this in fear of their cloud project being labelled a failure. Every person I have spoken to for months is hiding little pockets of pain under a banner of success. Some people clearly will never deliver and burn mountains of cash hiding this.
3. Once you enter an ecosystem, you are at the mercy of the ecosystem entirely, be that a service provider or a tool. Portability is always valuable. It has cost, scalability, redundancy and risk benefits far beyond the short term gain of a single vendor decision. I'm currently laughing at an AWS quote for a SQL Server instance with half the grunt, no redundancy, no insight possible for only 2x the capex and opex combined of dedicated hardware including staff. But can't move to Azure because everything is tied into SQS.
I can never be behind anything but IaaS myself. This is contrarian especially in this arena but I will put my 25 years of experience on the line every time and say that it is the right thing to do. IaaS is choice, flexibility, allows you to gain deep insights and protects you from serfdom, fad technology and pick and choose mature products rather than what the vendor sees fit.
This is just another rehash of buying a mainframe. It's just bigger and you pay hourly to write COBOL.