It depends a lot on where you want to work. I'm mainly talking about the US job market here.
If you want to work on the cutting edge, work for the 'cool' tech companies and so forth, you won't find much so far as Microsoft goes.
However, if you want to work within the much larger corporate IT world, then the Microsoft stack is a lot more common than anything else else. There are a huge number of in-house legacy applications that businesses depend on daily.
For example, where I work, a 20 year old VB6 app that's been patched and enhanced nearly to death is what keeps products going out the door. There is also a patchwork of C# .NET apps, desktop and web, running. Keeping them running is more important than replacing them. This means that the service API replacement project moves along very slowly. About 3/4 of our sprint capacity is spent on supporting these legacy applications. Many companies are in this situation and this creates massive opportunities.
For someone of middle age and beyond, having this skill set is a significant hedge against the rampant ageism in tech. This would also apply to women and non-Asian minorities who also face significant discrimination in the 'cool' tech world. For people who work on offshore teams, knowing the Microsoft stack creates considerable opportunities when US companies can't find enough people to fill contract roles.
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