Why do cars in motion seem to stop moving when I'm looking at them from high altitudes e.g. aeroplane?

The cost in designing, developing, and testing an aircraft is staggering!!! Defense contractors as those you mention have extremely strict regulations to follow regarding export control and no equipment is sold to a foreign government without the express approval of the US gov't.

You're stuck with a water landing (ditching). Hopefully at altitude the pilot can see a ship and make the landing in the vicinity of the ship for quick rescue. It so rare for a plane to lose power to all engines though that you should never hear of such an incident. Depending on the route, however, Bermuda may be within gliding distance.

its all about relative motion and being part of the earth atmosphere system, the plane is matched in speed with the earth. its the same reason we dont fly away when we jump up.

Your question is a good one - but the answer is much more complicated that you would expect. Think about driving your car from point A to point B across a city. Lots of paths - some shorter than others, but the shortest path may not be the quickest. Or the quickest may involve a toll road - and you may or may not be in a hurry.

The usual most important factor (for commercial operations, at least) is to save money, while still arriving on time. Airplanes in the air are subject to the winds aloft, which will generally be at different strengths AND DIRECTIONS at different altitudes. Most airplanes operate more efficiently at higher altitudes (up to limits), but at those higher altitudes the plane may face stiffer headwind. Further, it costs time and fuel to climb to those altitudes, and you will not regain coming down as much as it took going up. [Think of a bicycle on hilly terrain vs. level ground.]

So what's the answer? Well, for most trips the pilot will consider all these factors. They are taught during training how to plan the flight in terms of time and fuel required, and to include in that especially the winds at different altitudes. Then they will pick the altitude, whatever that is, that maximizes the results that they consider most important.

Depends on aircraft and altitude.

That would be the ground prox system on the aircraft it lets the flight crew know how far they are above the ground during an approach to the landing runway.

Departure controllers have blocks of airspace with altitude limits. Chances are that there was other traffic that they needed to have out of the way so they held him at 5000 before clearing him to the next controller's airspace.

I suspect that the idea of max climb plus glide is not a new one, and that, if it really were cost-effective on fuel, we would know about it.

Aircraft too heavy. Weight is extremely valuable/expensive and the weight of a parachute system would be too heavy and costly, sacrificing room for paying passengers.