I'll do mine: there's likely a correlation between needing to maintain a professional conduct which includes forgoing foul language (you're programming at work) and writing code under time pressure where getting a product ready for release is more important than strict adherence to clean programming practice (you're programming at work).
Everyone post your favourite conjecture!
Take almost any two things like this and you're actually virtually guaranteed to draw out some weak, but quite likely statistically significant, correlation.
What lies behind that correlation is probably a entropic mishmash of so many factors that it defies human explanation, and also, defies any attempt to try to "harness" the forces that seem to appear. It could be that all the siblings to the comment are right all at once.
I'll cop to just glancing at the graphs, but they don't look out of line for this effect to me intuitively.
Also backing this is that more-or-less the same article/thesis could easily have been written for the opposite correlation.
Places uptight enough that developers never swear in comments are uptight in other ways that lead to poor team dynamics which hinders quality.
The other extreme: if you have no idea what you are doing, you might try to mimic "corp speak" in your code to hide the fact that you actually have no clue.
In other words: it needs some confidence in your ability to assess some aspect of the code in order to use swear words.