Zipline's platform 2 is VTOL and is essentially a quad rotor + 1 rear swivel motor, during delivery. A fixed wing won't help you much if you have a failure while hovering. Google's Wing is a very similar design (6 hover motors on a boom, two booms, one along each wing). The key is flight system redundancies, something consumer drones simply don't have, and Zipline also has a ballistic parachute in case of severe failures since their aircraft is fairly large.

Maybe they won't ever become a "big thing", but Zipline is already delivering food directly to consumers in TX and elsewhere.