Joe, yes, good point. I mean its called a PRIVATE jet for a reason.
However, psychology is a strange thing. One has to ponder which end-user segments are these guys are targeting. Many popular products and services today are logically ridiculous and should be repulsive, yet many people love them. It was like that with LOCOS when they were starting - the central argument was that the "no frills" model will never work, because having in-flight amenities and food included in the ticket was an industry standard. And yet, here we are today...
In reference to Jetsmarter, as far as I understand they flopped not so much because it was 6-7 stranger sharing the jet, but for the fact that they effectively promised one thing but delivered another: the fixed membership fee essentially turned what was promised to be the pay-per-seat business jet service into just another fractional ownership scheme. And then, of course, too frequently they could not deliver on-demand. Hence, the customer felt cheated. I think that was the main issue.