Step 1: Release cool FOSS apps and gain popularity.
Step 2: The apps are still FOSS, but now most of the cool features are actually proprietary and running on the company's servers. <--- we're here right now
Step 3 (soon-ish): "Since our customers love our proprietary features so much, we're no longer maintaining our FOSS version. Subscribe to our new pro subscription to continue accessing the apps"
Honestly MS doesn't even both hiding the fact that they want to you to use Windows so they can sell you subscriptions to proprietary software and the cloud.