Purpose built vehicles, economies of scale, gov-industrial complex support, and Wall St buy-in are a few that come to mind. Not to say that the SureFly is inspiring to look at, but priced less than an R22 with no single point of failure design and a ballistic recovery chute? Game-changer if it can get certified.
And who will certify such a vehicle? One that is driven by a computer link to some program, perhaps by encrypted link. An astounding amount of testing will need to be done to show that an air vehicle can get itself from Home Base (storage) to a pickup point and land, somehow know that its passengers are on board, and that they are the pax who ordered the flight, not just queue-jumpers, and fly to a requested destination, land, let the pax out, ensure they are clear, and return to home base for a recharge. If it is all done through an app on their phone, then the whole show can be hacked.
The vehicle will require testing to ensure that it can still carry out its job of lifting 6 pax, even if a percentage of its motors are inoperable. On takeoff, if it suffers more than a critical number of motor failures, at what altitude can it fire the ballistic parachute, and will the load then drift off a building top to crash into the street hundreds of feet below? Not to mention that it doesn't have a heroic pilot to steer it away from the school filled with terrified kids. Crashworthiness. Battery safety. Air con. Some way of ensuring the passengers aren't goofing off without seat belts, trying to tip it past its CG, all leaning to one side to see the Grand Canyon or Golden Gate.
These tests will cost stultifying amounts of money, which then has to be recovered by the cost of the craft, which is passed on to the travelling public. Cheaper than an R22? Fuggeddabahdit.