Two thoughts:
I don't think this will be very popular discussing other teacher's techniques on this website, but I seem to recall hearing Freddie Spencer mentioning on TV that since trail braking steepens the bike's steering geometry, it allows the rider to change direction more effectively (i.e., run a tighter line to change direction quicker) and, hence, get on the gas sooner.
Another thought is: perhaps a reason why fast guys trail brake is to carry their speed from the previous straight longer by compressing the braking area into the shortest possible distance (at a later point) as close as possible to the optimum point where re-accelerating should begin.