Stack Overflow existed for a couple of years before taking any funding and it was developed by three people who were friends (Jeff Atwood, Jarrod Dixon and Geoff Dalgas) none of which were even getting paid regularly at the start and who were all primarily familiar with the .NET stack from previous jobs.

It makes total sense why the tech is what it is. One could argue they could have shifted away from that stack since then, but one could also easily argue (very convincingly to anyone who has ever been involved with any significant project rewrite) "but... why?".

That's a reasonable point, but still is the cost of the licens higher than the cost of one or two additional developers? Jeff Atwood was/is if I recall a pretty talented C# developer, so why onboard extra people. It's more than just their salary, there's a cost beyond that associated with hiring people.

I'm not arguing that the licens isn't a concern, I just question how much of a concern it really is, compared to everything else.

The MS stack is affordable to developers working on developing countries and free for small products (with a lot of strings attached).

Of course, the OSS stack costs nothing to acquire, is cheaper to admin, and will give you more functionality and easiness of use, but the MS one isn't some unaffordable monster like other proprietary ones.