The answer is "because Microsoft could conceivably lose deals in the event that it sets costs unpredictably".
Microsoft Corporation shortened as MS, and it refers to an American multinational innovation or technology organization with home office in Redmond, Washington. It creates, makes, licenses, backings and offers PC programming, shopper hardware, PCs, and administrations. Its best known programming items are the Microsoft Windows line of working frameworks, the Microsoft Office suite, and the Internet Explorer and Edge web programs.