Honestly, with any vendor not named AWS, it's incredibly difficult to parse their actual "cloud" revenue. I believe Microsoft bundles in their Office 365 revenue just as Google does Docs. IBM stuffs in all sorts of seemingly unrelated stuff to make their numbers sound bigger. It's actually difficult to compare apples-to-apples because of all the gamesmanship.

Companies think they are simplifying things by using Azure since they already rely so heavily on MS software. That's pretty much the only reason Azure is more popular. GCP is a far better platform.

Not so sure about that. Their infrastructure is highly customized down to the PCB. They were designed in-house for Google's workloads, AFAIK.

Did Amazon have the same constraints?

Apparently not. According to Steve Yegge's letter about Google+ (copy at https://gist.github.com/chitchcock/1281611), one of the mandates Jeff have asked is to ensure that "All service interfaces, without exception, must be designed from the ground up to be externalizable. That is to say, the team must plan and design to be able to expose the interface to developers in the outside world. No exceptions.", while on the same letter his impression of Google is basically on the other side of Amazon's spectrum, even describing how bad Google's documentation at the time compared to Amazon, Apple, Facebook and Microsoft.