Why is it so difficult...

I've done a lot of searching for an interface between my iPod mini and the '06 Prius and have come up with nothing that will display text on the LCD screen.
I've got the nav system and just want to have the text info on the display as well as steering wheel control. Too much to ask?
I've looked at and have called Vaistech LSI, Dension ice link +, and also Axxess for the Wire-Tunes. None of theme show any indication they have or will come out with anything compatable any time soon. What gives?
What is the problem with the interface communicating with the iPod and the OEM stereo?
signed,
Frustrated in Fremont.