I sympathize with MSFT, but the main reason they shouldn't unilaterally force the issue is because it won't always work. The upgrade process is pretty reliable, but not completely, and there are all sorts of compatibility problems still lurking (Windows Media Center is gone, lots of hardware doesn't have Windows 10 drivers)

Google is taking the longer view; they want to fix fragmentation, and are moving towards it step by step, improving matters on tomorrow's devices, without bricking today's devices. MSFT is trying to make it happen sooner by forcing the issue instead of gradually migrating.