Once a paper gets big enough you basically have to cite it any time you touch on vaguely related just to prove that you are aware of it, almost as a shibboleth. My wife is an academic and on more than one occasion has she gotten comments back from peer review along the lines of "good article, but you why haven't you cited famous papers X,Y and Z".

I really appreciate this practice. It makes it much easier to get up to speed on something new.

That somehow reinforces that publishing source code with CS research papers is more than necessary :)

Indeed, it makes me wonder if published code leads to higher citation counts.

Although if it does, I suspect it has more to do with the fact that there's a product & marketing around it.

I wonder if it's more subtle than that - if your paper has associated source code, then it's likely that people reading it might try it out, and the ideas that you've presented will stick around more than a short paper with no follow up material.

In other words, papers are only a short glimpse into your research, presenting code allows an interested reader to look deeper, and means that they're more likely to remember what you've done, and cite it later.