Most piston twins have carved themselves a market share for a few years, then vanished as market conditions changed. Piper’s Twin Comanche and Aztec are examples and so is the Beech Travel Air, Duke and Duchess. On the other hand, for various reasons, some twins have endured and Piper builds two of them, the Seminole and the Seneca. Both have endured for various reasons, although neither is made in much volume these days.
It’s easy to see why the Seneca has endured. It does nothing exceedingly well—it’s not fast, nor a joy to fly nor will it turn heads on the ramp—but it does a lot we’ll enough.