That is a technique that is often used to impose frugality and get savings [1] out of the rest of the execs by setting an example. If he flies coach well then so do a hundred others.
[1] I knew a guy who owned a small company and bought a low end car until he had locked up his union contract. He knew if he was seen with a nice car it was going to cost him a boat load.
Likewise in my old school company years ago I never even drove up to the business in my nice car and I went out of my way to hide it's existence. It goes along with staying late and arriving early to set an example.
I'll take Uber pools, walk, or take public transit even though I'm technically no restriction on my transportation spending. Likewise, unless I'm taking my team out to dinner, I'll usually grab a $10 gyro or something instead of going to a nice restaurant.
> 'The other thing is that I sometimes use a private jet. It does help me do my foundation work but again it is a very privileged thing to have.'
He inserts the word 'sometimes' to lessen the impact of 'private jet'. He adds that it helps him do foundation work implying that that should make it ok in normal people's eyes. [2] He doesn't mention that it's actually importantly needed for security purposes he is obviously a target and not flying like the general public. He then acknowledges that it's a privileged thing to have.
[1] Remember the movie "An Officer and a Gentlement" when Lou Gosset character fights Richard Gear character? And Gosset character replies (something like) 'oh I see you've had some training!'. Well Bill Gates has had training.
[2] Which is should be anyway. Without saying that.