[dunham]

It's been a few decades, but I recall having to write in all caps in my high school drafting class. We were told the all caps and the letterforms we were told to use helped legibility when the drawings are stored on microfiche.

[retrac]

We were still taught that in high school in the late 90s. Probably some of the last. You are correct. Here's a good example of drafting from the 1960s: https://i.imgur.com/tXozAMy.png

It's not just all caps, but a flowing, easy-to-read style of all caps.

Hard to believe people used to draw all this stuff by hand. I was never very good at it.