The sheer numbers are for the legions of ho-hum programmers building CRUD data-entry systems for e.g. aluminum can factories. The majority of startup-oriented engineers are a different group and I agree that .Net may be off-putting to them.
Also the vast majority of startups not building tech can get by with basic CRUD like apps for most of their business processes. Whatever gets you to market fastest. You will end up rewriting everything 3 times over probably in your company's life as I've learned but you won't get to do that unless you ship something.