Because it's a cherry picked example that ignores a lot of factors.
I could easily make the statement "Microsoft gets a cut of everything purchased on Xbox, why shouldn't Apple?"
To which I suspect your response would be waving your hands around something that is ill defied (General Purpose Computing), and then trying to define it to fit your narrative.
A more cogent and principled response would be that there is an effective duopoly in the phones market, and this creates incentives for and actually realized anti competitive practices on the part of both google and apple. Apple both builds a market and regulates that market in its own favor, and consumers don't have an especially plausible alternative to participating.
Microsoft chose to create Windows as an open platform where they didn't get a cut of application sales.
Microsoft chose to create XBox as a platform where developers who didn't pay them a cut could not sell software.
Microsoft attempted to convert Windows into a platform where developers who didn't pay them a cut could not sell software with Windows RT, but it failed in the marketplace.
A more fair comparison would be andorid. Or the Windows Phone, where Microsoft took 20%: https://en.wikipedia.org/wiki/Windows_Phone