This is such a bizarre thing to do from a young man/evolutionary instinct standpoint. I wonder if his hormones were awry. I see speculation that he had hypogonadism or phimosis.
Maybe he had depression from this kind of passive lifestyle.
https://en.wikipedia.org/wiki/Louis_XVI#Marriage_and_family_...
Made perhaps even more likely with Antoinette's alleged proclivities, her children's questionable paternity, and so on.