I'm going to guess...
In the Excel world, there are so many tools available to do things. Couple that with the fact that, in my experience, so few people are really trained on how to use them correctly.
The biggest single issue, though, is that so many people don't realize that what they have built is not easy to audit, maintain, or understand for someone else. Why? Because they're so deep into it, they know how they built it, and they've always done it that way. And possibly it also starts as a project for their use only.
As an aside, I'll bet that the person who built an entire sheet of array entered formulas thinks that they're quite clever, actually! LOL! (Boy did it ever stump me the first time I ran into one of those!)
