It's because they make their devtool money off of enterprise licensing costs, and they get those costs by getting developers to be okay using their devtools.
The tool is the advertisement for building software for Windows. If it gets too miserable to use the tools or build for the ecosystem, then some companies won't prioritize windows software, and developers will prefer jobs doing something else. It's got to be good enough so that decision makers at software companies don't start hearing that windows software takes three quarters longer to develop.
Web developers are already targeting their browser as an afterthought, and mobile developers are pretty pulled into to apple ecosystem, since you can develop android apps on a Mac, but you can only use a Mac to make iPhone apps.

Without developers, applications lag, and they lose business and consumer market share, which costs them more developers.
Hence: visual studio is fine, and they keep adding azure features to GitHub and tying it all to visual studio.