Because as more attention/money goes to other tech ecosystems, it weakens their position in the market. The computing world used to revolve around Windows/Office, now it's increasingly a tangential legacy player. It used to be that you bought a Windows PC to run Office and other Windows apps. These days it's just the way they get to the web for many... and only on desktop/laptop devices. Microsoft knows they have to remain relevant or their future will increasingly look like Intel's.