They have a widely used desktop operating system, a top-3 public cloud, they make their own laptops and other hardware, they make multiple widely used programming languages, they have one of the most widely used databases, they have a well regarded research division ... the list goes on
The scope of tech that MSFT works on is as big as anyone, and is what they primarily make their money from ... so why wouldn't anyone think it's "big tech"?
Disclaimer: I do work for Microsoft on SQL, but I am not in management nor do I speak in any capacity for Microsoft.
and so it's not seen ad big tech, even if it's used by more people.
maybe it's also because MS tech talks don't really make no1 on HN.
Loud people do not always reflect reality very well :)
They have sustainable business models in several segments, and even though they aren't on the cutting edge of pop culture, they're doing well.
One thing about Microsoft, their tooling just seems more polished and things tend to just work.
I'd be surprised if a lot of start ups don't start using c# since it's now open source and more platform agnostic.