Because we need to think realistically, and economically. Improving, and incrementing familiar technology now. Not introducing another mess in the air. We haven't even got self-driving land vehicles, and we're just going to make the jump to aircraft that NO ONE is familiar with? We still rely on primitive controlled explosions to get off our planet. Sure it's a neat idea, but this isn't the Fifth Element world yet.

Update ground infrastructure, improve public transportation, make renewable energy a priority, get our cars driving themselves.

In theory, we might develop a vertical-liftoff flying fully-autonomous car, that starts anywhere and brings you to the free parking spot closest to the target. We would have to overcome some safety challenges, and convince society that it's safe (to even enable the needed reforms in airspace regulations).

Now even if we did all that, with current technology flight is both incredibly noisy and less fuel efficient than driving (commercial airliners are primarily efficient because hundreds of people travel in one vehicle).

It's not really a physical limitation, after all maglev trains gain fuel efficiency and noise reduction by floating. But our existing technologies for free flight just aren't good fits for cars.

Cost and safety.

^ This. Think about the capacity constraints during your typical commute. All those times you have ever been held up in traffic could be massively diminished thanks to increase short-hop flight commutes.

+1. Fliers can solve commute hell. Every building has roof, which can be used as a pad for fliers, which will solve problem with parking.

Nuclear batteries can provide enough electricity for flier for years. We just need to develop safer nuclear batteries (LENR type?), which, in turn, requires better understanding of nuclear physics, which, in turn, requires to shoot some «shut-up and calculate» guys.