There really is a wide gulf between the services provided by the older cloud providers (AWS, Azure) and the newer ones (fly.io, CloudFlare etc).
AWS/Azure provide very leaky abstractions (VMs, VPCs) on top of very old and badly designed protocols/systems (IP, Windows, Linux) . That's fine for people who want to spend all their time janitoring VMs, operating systems, and networks but for developers who just want to write code that provides a service it's much better to be able to say to the cloud provider "Here's my code, you make sure it's running somewhere" and let the cloud provider deal with the headaches. Even the older providers' PaaS services have too many knobs to deal with (I don't want to think about putting a load balancer in front of ECS or whatever)