I agree with the profit/control motivations the other posters mention, but there are other less anti-users reason as well. Agreeing on a common API mostly lock

I agree with the profit/control motivations the other posters mention, but there are other less anti-users reason as well. Agreeing on a common API mostly locks you into the common denominator of features. It becomes much harder to ship new capabilities to your customers if you also have to add those features to this standardized interface and get all the stakeholders to move forward with it. All these platforms have some features that their competitors lack and it'd be quite the challenge to expose each platform's unique features in a standardized API. Email (IMAP/SMTP) is a success story of a widely adopted standard, but it's also something that has barely changed in the last 15-20 years partially as a result of its standardization. You can tell IMAP is cumbersome to the modern developer. For example, you'll have an easier time working with a gmail account by using the gmail REST API instead of trying to use IMAP. (IMAP has more limited search support, lower-level thread support, and less specific support for syncing clients)