Another thing that surprised me is the recommendation to flick corner entry in to full lean in the shortest amount of time possible, and so far at least in the book it doesn’t seem to address trail braking at all. I would think slower corner lean at a speed fast enough to require some traction to remain available for trail braking would be faster overall and less “surprising” to the tire. Perhaps that is just my car experience, but trail braking is huge in a car, especially on tight corners.

The reason for this is to minimize the number of "steering actions" that the rider has to make. The steer itself is applied via a countersteering force. Once you have made the steering action, you should not need to make any more.

A way to think about this is to look at the ideal cornering line. For a motorcycle, it is more angular instead of perfectly circular. This is because you "tip" the bike over with a singular steering action.

https://lifeatlean.com/wp-content/uploads/2012/04/images_LateApexRacingLine.jpg