after working at a cloud provider, I would say:

1. managing compute clusters has gotten a lot easier but managing storage clusters and running good storage products for block & object storage on them is very very very far from a solved problem and quite frankly it sucks and is not fun.

2. planning out buying, installing, upgrading, patching, and retiring hardware, server/hypervisor OSs, takes waaaaaaaaay more engineering management skill and experience than 99.9% of companies have. Plus you probably have to fight for every dollar of investment against a board / investors. Even at the cloud provider we were constantly getting kneecapped by upper management not wanting to spend money on hardware.

Yeah calling the EC2 API is definitely more complex than leasing datacenter space, purchasing racks of hardware, deploying a fault tolerant and secure network, capturing and managing offsite backups, dealing with hardware component failures, etc.