Money: most projects didn’t have enough investment. Brin presumably can handle a conversation that starts with “We need another billion for…”

Wind patterns are actually well understood: hot-hair ballons already move around simply by changing their altitude and going around reasonably freely. I don’t know if those could handle the jet stream, but that would make NY-London a lot faster.

Agree with you on how slow previous prototypes have been: I was part of a project that tried to use them for urban transport, and it was not going nearly that fast… 65 knots is the speed of cars on a highway (at least the legal limit).

> So often tried never successful. What si the difference now?

It's fortunate the Wright Brothers didn't listen when the guy at the Kitty Hawk bar said that.

The key answer was “a more energy intensive power source and better aerodynamics”.

Also, the question is not whether a big airship can be made to fly, because there’s little doubt they can. The question is whether a business model exists that can pay for their construction and operation.