I have no idea if this is how it works, but I imagine someone at Garmin must have said, "Hey, why don't we just yank the radio out of the GTN navigator and stuff the rest of it into a standard rack-size panel box? Put a pretty display on it." Maybe someone at an avionics shop suggested it. Wouldn't have been me, because I'm too much of a dullard to appreciate the potential until it's explained to me. And maybe not even then.
This is a companion discussion topic for the original entry at https://www.avweb.com/ownership/garmin-closes-the-deal