People love admitting that Microsoft is no longer the biggest player there is, but they hate admitting that the other players are just as bad as Microsoft apparently were in their long history.
Selectively withholding services can easily fall under anti-competitive laws in the EU. Microsoft is not asking Google to make an app, it is asking for the same levels of access as iOS so that Microsoft themselves can make a better app.
The only way a phone OS gains traction these days is app support. If services selectively deny app support for phone OSs by not producing an app, that's probably fine as the business case would be there for "not enough users". The indirect effect is the OS won't gain any traction without the app, vicious cycle. To combat this cycle, they front up the cost of making the app themselves for their own platform OS, great. However, in this case it isn't great because they are being blocked by this route too. Closing all avenues to offer the same level of app integration is anti-competitive.
Comparing this to MS offering Office on Linux isn't the same. MS offered the access to the file formats, allowing others to produce competing, and most importantly inter-operating software alternatives. I use both Office and LibreOffice on the same sets of files. MS have not been given this luxury from Google yet Apple have.