There's a lot less shifting than you might think. Really depends on the bike. A 250 depends on keeping the revs up, so you shift more than you would on a bigger bike that has more torque.
Every shift is a potential source of error (even Ken misses a shift in this video, and he's
good). It also interrupts your drive and potentially upsets the chassis if you're not smooth, both of which slow you down.
Finally and perhaps most important, shifting a lot adds workload that you don't need (trust me... at speed, a whole lot of your brain is occupied with just riding the bike).
I don't recall how often I shift at NHMS, but it's about the same as Ken. Probably less, because he's a lot faster than I am.
At Thompson, he (and I) ride the whole lap in one or maybe two gears except for the straight (he currently rides a Street Triple, I ride an R6).
Check this out:
Link to original page on YouTube.
Same at Palmer, more or less.
When you're a new track rider, it's common to over-slow for corners and try to make up for it on the straights. There's a greater difference between your fastest and slowest speeds. So you feel that you need to shift to get more drive out of the corners.
As you gain experience and skill, you carry more speed through the corners, so less need to downshift.
There's also a lap management aspect to this. At Palmer Turn 1, the "right" gear is to go from 6th down to 2nd, because TTD sets up a chicane just after the turn to manage speeds down into Turn 2 and keep people from splatting themselves against a giant, scary rock wall.
The chicane is slow. BUT right afterwards, the track dives steeply and bottoms out at Turn 2. Your speed comes up fast, so you'd be upshifting again almost immediately anyway.
So the smoother way through there (which I found through experimentation) is to take Turn 1 and the chicane in 3rd gear... less herky-jerky power delivery from second-gear engine braking... and hammer it down the hill. Your momentum is plenty to carry you through the chicane. Less drama, more speed.