[Dewie3]

Non-standard character set aside; is the terseness (one-letter commands and such) partly because of the slow input devices at the time?

[Avshalom]

The terseness is because it was originally developed to be written on a blackboard while lecturing.

As CS developed in the math world Iverson realized that the existing math was crap for describing computational processes. So he made his own and as it turned out it, with a little modification it was executable.

[mollmerx]

I believe it's more likely to be partly related to the small console sizes that were typical at the time.

I don't think typing was slower then. And most programming time isn't spent typing.