They are just old school. When you learn coding before GUIs were mainstream, you don't care that much about exciting UIs.

Heck, Kernighan was one of the original developers of Unix. In 2015 he was already coding for more than 40-50 years, more time than most from Hacker News are alive. The only constant from that time is the terminal, so no wonder most people in the post gravitate towards that