Microsoft is indeed private sector. However, Microsoft is public in several other ways, which invite regulation in Slashdot's home country:
1. Microsoft is a publicly traded corporation. This is regulated by SEC.
2. Microsoft sells hardware products to the public. This is regulated by CPSC.
3. Microsoft operates websites used by the public. This is regulated by an army of private-sector civil lawyers that enforce ADA.
4. Most importantly in this case, Microsoft has a monopoly on desktop computer operating systems in Slashdot's home country, and the Department of Justice has already prosecuted Microsoft for leveraging that monopoly to unduly promote Internet Explorer (now called Edge) and MSN Search (now called Bing) to its Windows customers. United States of America v. Microsoft Corporation, 253 F.3d 34 (D.C. Cir. 2001). A repeat offense could land Microsoft executives in jail come the next administration.