You do occasionally see very simple, rudimentary trapping. Author/analyst Jack Slack has produced some material on the subject:
http://fightsgoneby.webplus.net/article01.html
http://fightland.vice.com/blog/wing-chun-and-mma-controlling-the-center
https://www.youtube.com/watch?v=WAVxYY0hf-4
You see techniques that are analogous of Wing Chun's jut sao, pak sao, and lop sao, as well as the "beat" (a fencing technique that Bruce Lee adopted to JKD's empty hand work) and techniques that are called a "smother" in boxing or "checking" in Parker-lineage Kempo.
The thing is, the window or opportunity for such techniques is usually a small one. Also, because of how trained fighters actually fight, you're not going to see the "compound trapping" show up- using multiple traps in a single sequence. You also have to remember that the way trapping is trained in Wing Chun basically relies on the other guy engaging in a Wing Chun battle, and that JKD may use an artificial construct (a high "reference point", a la the Enter The Dragon fights, which hardly ever occurs in real fighting) to train its trapping sequences.
So trapping shows up from time to time, but it doesn't look like Wing Chun or JKD demos because those demos don't reflect the reality of how people actually fight.