Old habits die hard. I still occasionally see some engineering veterans who use the capital letter "S" for seconds (and they would write "nS" instead of "ns" for nanoseconds) - even in chip datasheets. And when I was reading a textbook one day, I also noticed that the author, an expert with a life career at Bell Labs, just couldn't write MHz properly, and instead wrote "Mhz".

In their time, Siemens and Hertz had not even been added to the SI system yet, I imagine they would speak in terms of mhos and megacycles back then.