Kernighan has always used troff, so it is not a surprise that he is still using it. He can do things with troff that most people would have a hard time to do wi

Kernighan has always used troff, so it is not a surprise that he is still using it. He can do things with troff that most people would have a hard time to do with LaTeX. On the other hand, this doesn't mean that troff is better, in fact as you said it has not been updated for a long time. For someone starting now, it is so much easier to learn and be productive with LaTeX instead of troff.