It's possible to find a piano accordion with piano keys on the right hand and the triangular arrangement of buttons on the left-hand. It's also possible to find a button accordion with the triangular arrangement on both hands and a free-bass system instead of the Stradella system. The bayan is a 20th century solution to the centuries-old quest to find a portable, sustained-note keyboard instrument.
The obvious other way to go is to have piano keys on both hands. In some ways this is a more obvious instrument to me than a bayan, given that the piano keyboard is already a thing. There are obvious problems around playing piano keys freely with the hand that's controlling the bellows, but perhaps not insurmountable. Has anyone ever made such a thing: a piano accordion with piano keys on both hands? If they did, what was wrong with it: why didn't it catch on?