I don’t know that this is a reasonable generalization. Certainly in my CS department one could write a thesis to receive an MS, and no MAs were offered. Just one data point, from a very large state school; YMMV.

You're correct, it's not a reasonable generalization. See my reply above.

The essence of my answer is based on the way things were in my graduate programs at my university when I was in school there; and some observations from so-called terminal Master's degree programs.

I should clarify that the M.S. is available in some departments as a terminal degree, or is awarded along the way towards a Ph.D. upon completion of coursework and admission to candidacy (oral/written exams), as is the M.Phil. The main thing is knowing what the degree was awarded for at the end of the day, which may or may not matter to the degree holder or the employer.

In my doctoral program in chemistry, the M.S. was "awarded" to Ph.D. candidates who did not pass orals and was referred to as "the booby prize." Having been admitted to candidacy and completing my doctorate, I have only a Ph.D. in chemistry and not a Master's of any kind.

Having said all that, almost every M.S. I've seen during interviews over the past 20 years has been a terminal degree lacking a thesis - but I am a scientist, and I see mostly physics/chemistry/geology/mathematics resumes and not engineering or CS ones.