David Crane, the creator of Pitfall, explains it all very nicely in a GDC Classic Game Postmortem [1]. I'm linking at the relevant timestamp, but the whole video is pure Atari 2600 goodness. The full Postmortems playlist is quite enjoyable too. I particularly liked the talks about the original Deus Ex, Myst, Loom, Adventure, Marble Madness, Ms. Pac-Man, Paperboy, Lemmings, and more. I find these videos very soothing and nostalgic. Got to rewatch them now...
[1]: https://youtu.be/tfAnxaWiSeE?list=PL2e4mYbwSTbbiX2uwspn0xiYb...
It isn't as if you could have a map editor and adjust the levels or the order of the levels, though you could run the generation procedure to find new levels to your liking.
Still an amazing game. In 4k it is astonishing.