Oh, I don't know, there's something neat about building something with so many layers of complexity given such tight constraints. "Making every bit count" I guess. Similar to it being impressive that Pi and Following were made with such small budgets (and casts).
I'm not sure what "exceptionally challenging" means exactly, but Lucas Arts was doing something very different from what their contemporaries were doing, and their games still stand as classics twenty years later compared to the much larger budgets and fewer constraints of today.
It always confuses me when people are impressed by low-res graphics having an emotional impact.
I read novels. I played text games. Graphics merely seem like yet another genre to me, not something exceptionally challenging.