Your question is of particular interest to me, because I have the accepted and highest upvoted answer on the example of a programming question (one about optimisation) you think should be on Stack Overflow.
Here is a similar question on Stack Overflow. Someone actually made the point I want to make in the comments: "Optimizations depend on the context". You have to go half way down the page to find a brief mention of cache coherency - something to which I dedicated an entire (and seemingly very popular) answer. Clearly, for some programming questions, context is important.
The kind of programming problems that come up here on the GameDev site (example of mine) are very different to those that come up on Stack Overflow (another example of mine - game related but better on SO). Or at very least should do so.
And obviously there will be some fuzzyness. And it would be good if we had a way to punt questions between the two sites. But that is a small price to pay for the value of having a pool of domain-specific knowledge on this site.
(And it almost goes without saying that there are many other aspects of game development - art and business to name two big categories - that are clearly not suited to Stack Overflow).