Surely it would be easier to kidnap a passenger at their hotel, or to hijack their taxi, then to steal an entire airplane, take control of hundreds of passengers, make it disappear from radar, spoof the location, fly it across national borders, land it in Kazakhstan, and hide it underground.

It's completely absurd. If the president of the United States was on that flight, I'd give it more credibility. However, which passenger on that flight was so valuable, and surrounded by so much security, that hijacking the flight made sense?

The same goes for cargo, it must be easier to make friends in the right places, or pay people off to have that cargo "misplaced".