Because when we're talking about CS education, it's usually in preparation for a software engineering career. Whether that should be the case is another story, but that's the reality.
There's some courses that are inarguably fundamental, some which "separate the good from the bad," but there's also many which are simply not practical, besides the fact that they teach you how to learn.
It's a flawed analogy but I'd liken it to mechanics vs automotive/manufacturing engineers. There's a good bit of overlap, but lots that isn't shared. And software engineering as an industry doesn't always do a good job differentiating between the two