...How is that a reason? Did people treat it like it was never gonna catch on and I never noticed?
The original GBA was pretty awkward. It was clunky, the screen was hard to look at (though it was an issue with past gameboys as well), and it all around just wasn't all that special (edit: at least in my opinion). I had a friend that had one, and I'd played it enough to not really like it. The SP, however, was awesome. It took everything about the original GBA that I didn't like, and it fixed it.
The only bad thing about the original GBA was the lack of a backlight (which was pretty bad though). Otherwise, it probably had the best design of any handheld. I miss those shoulder buttons.
That being said, my biggest complaint when they came out was the lack of day and night. It was a big feature of Gold/Silver/Crystal, and it seemed weird that they'd have gotten rid of it. I've long since gotten over it though. It's a pretty miniscule issue, and so I've let it go.
http://www.youtube.com/watch?v=RMnhk26J1bM (Proof that Superman and Sephiroth are one and the same.)