Yes, the Basic Rider Course is really basic. I had never ridden a motorcycle until I took the course, and I didn't even understand how sequential shifting worked. Most of the people in my class were longtime riders who were taking the course so they could get their endorsements and ride legally.
The point being: The course is for newbies.
It's a few hours in a classroom and a few hours on the riding range. You can't teach everything, and trail braking would have to be way down the list. It's more important to learn how to swerve, how to run over a 2-by-4, how to maneuver in a parking lot, than to learn how to trail brake when the time is so limited.
No one taught me how to trail brake. When I finally learned what trail braking was, after riding daily a couple of years, I realized that I had been using the technique for months. It's just braking late and easing up on the brake while you're in the turn. As you gain confidence, you just start doing it naturally.