I'm a new user on computer science stack exchange. However, I am confused about the reason why this site exists. Since stack overflow answers questions about programming, wouldn't it make sense to ask these types of questions on stack overflow?
See the help center for an overview of the type of questions that are suitable for this site.
As for why these question are not asked on Stack Overflow (SO), well, that was a common criticism back when this site was first proposed (see e.g. here for some history). Back then, the best we1 could argue was that there simply is a lot more to computer science than programming, and that many questions about computer science need a different culture and standards than a website specialized in questions about programming.
For example, SO requires a piece of code in most questions, while here, we often recommend against putting code in a question. Instead, we often want to know what the author of the question wants to learn or understand, rather than what they want to achieve with a computer program.
But now, you can see for yourself. Take a look at some of the many questions on CS.SE. Clearly there seems to be some sort of demand. Please look a bit closer as well, and compare them to some questions on SO. If you can understand both types of questions well, I think you should be able to see why they're asked in different places.
Finally, we're not even the only site in the SE network apart from SO that deals with topics in programming or computer science. See here for a list of most of them, with some explanation on how they differ.
1: Well, I personally showed up much later than that, so this is more a methaphorical "we".