The Powerbook Duos

I presently have(although I no longer use) a powerbook duo with a full 256-color greyscale screen, , and trackball(why did they ever stop putting these in laptops?) with the dock allowing it access to the floppy drive and 14.4k modem, along with full color.
I got it used and continued to use it till around 3 or 4 years ago.
Did anyone else have one of these?Its amazingly small and light, and far more funtional than a PDA, even now.

My question: Why did the concept never catch on?