On top of other answers, I'll add he balanced language power/complexity to make them easy to learn and compile super-fast. The latter boosted productivity by almost eliminating the waiting time compiles would give you in something like C++. Then, they'd crash instead of get hacked on many common errors. And if you needed, building a compiler for them was easy enough that it was a project for compiler students in colleges. Free Pascal, although more complex than those, is likely so portable partly due to simplicity/power ratio of Pascals.

Aside from Free Pascal w/ Lazarus, the closest thing to that experience today is Go language with Oberon-like style, safer-by-default, and fast compiles. One of its inventors stated a design goal was realizing the fast-paced, smooth experience he had with Oberon-2 in the past.