According to the latest news headline, Microsoft has acquired github for 7.5 billion US$. Would this result into a monopol in software development? No, because the monopol was there before the merger. A short look in the latest stackoverflow survey shows us, that 80% of all developers are programming exclusively under MS-Windows. That means, they have Visual C# installed and programming in the IDE C# apps, Python programs and Java apps. Only a minority of the programmer is using Linux or Apple operating system. On the github platform the situation is equal. Nearly 100% of all C# projects are written for the MS-Windows operating system, 99% of the C++ games, and perhaps most of the HTML5 and Python projects were developed in Windows too. So, if Microsoft comes to the conclusion to buy the portal it makes sense for the users.
In reality, Linux is not very common in the programming community. Worldwide around 5 million Fedora installation are out there. That means, core- Open Source developer which are using an Open Source operaring system and want to program an open source project are a minority. Github and Stackoverflow were never independent or Linux centric, from the beginning it was a Microsoft play.
Sure, some github repositories were created by Linux developers. That means, a MS-Windows operating system is not needed to compile, install and improve the sourcecode. And many repositories have an Android background. But, average repository has a Microsoft background. That means, the developer is sitting behind a Windows 10 machine and he programs in Java or C# which are both proprietary languages. I would guess, that most users have a problem with recognizing the reality. They want to believe, that they are hardcore Linux users, only because they have installed the Linux subsystem for Windows, but in reality they have absolutely no idea about Open Source software or the Red Hat ecosystem.
I think, it was a great move from Microsoft to acquire the number one Open Source developer platform, because this helps to compete with Red Hat. Otherwise, Microsoft would loose much more market share to the inventor of Linux.