Were Suntour TRIPLE pulley derailleurs only used with triple cranksets?

Looking at some old magazines and/or parts has me wondering about the Suntour Triple Pulley rear derailleurs. Were they designed to be used just with triple cranksets?

I suppose the idea behind that design was to have a short cage derailleur like performance when on the top two chainrings and then have that third pulley ake up the slack when using the inner third ring. I wonder why that design was dropped?

Cheers