Item — HN Reader

I guess it depends on how you view it.

Originally there was a Zork game, then a company was formed and they decided to repurpose their existing game as their first project/product because they had no other inspiration.

The existing content was too large to fit into the small computers available at the time, so only parts of the prior-art were used in the "new" game.

Zork [1] was popular so the idea of a sequel was raised, and of course the content which was left out was then used the second time around. And repeat.

I think it's fair to say there was no cohesive intentions to make three games initially, and you can kinda see that from the "plot".

The folks who wrote the original Zork were AI Lab folks who were generally more interested in the technology than the game design. They weren't really that interested in games as the end state. Which led to Cornerstone but that's another story.

And, yes, computer resources were a big issue. I think you can find at least one presentation from Dave Lebling (maybe?) at GDC where he talks about some of this.