Is this a shortcoming of the language, making it exceedingly difficult to focus on these traditional aspects, or is it just that the composers who would choose to use a tool like this are more likely to prioritize other aspects of composition?
It's certainly not a fundamental limitation of the language - CSound and its instrument libraries allow traditional note-based pieces with any kind of melody and harmony you like. In fact one reason I avoid CSound is that it's still a little too traditional for my liking - in particular, the similarity that i-statements have with the traditional idea of a 'note' with a certain duration.
However, the lower-level a tool you choose, the more work you typically have to do yourself to get things sounding nice - and it may be fair to say that "out-of-the-box", Csound instruments don't tend to sound as obviously pretty as the best patches on a typical VST or hardware synthesizer - and the workflow might not be as immediately fun as mucking around with those.
I would also agree that the priorities of a composer who has come to CSound might be atypical. But IIRC it's a fairly simple thing to set up a couple of instrument sounds and get some 'proper tunes' going. There are plenty of alternatives though when it comes to coding languages though - sonic Pi is one that I recently saw demonstrated impressively.