It would make an already dangerous sport even more dangerous. Also, just because it may be theoretically possible it doesn't mean it is practically achievable. Think about what would happen if the driver can't approach the loop that turns the car upside down with enough speed, or within the angle range that's needed for the car to stay on it because of another car, or some problem... Basically any small mistake would be fatal.

Imagine the leader car having any kind of issue at all, thus bringing the pack to a stop. The lift would disappear and everyone would fall to the ground. With nets it might be quite a spectacle but still safe!

Because you'd have to ensure you're going a minimum speed before that section of track.

Means you can't continue I'd you're slowed down for a yellow flag or someone threw you off your line.

The physics works, it just doesn't add to the race other than spectacle.

We should just go full Trackmania