Because whom-ever at the FAA that wrote this requirement is retarded. It is a worthless requirement, except perhaps as a bladder holding and excessive fuel-burning exercise.
A good work-a-round for the "VTF" deletion of waypoints outside the FAF is to load the full approach, then highlight and activate only the leg to the FAF. That's the segment you'll be vectored onto by ATC and you'll still be able to see all the fixes.
Don't beat yourself up. A lot of pilots have difficulty learning instrument technique and most deviations are either the result of a faulty instrument scan, or unconscious over-controlling. I've seen a lot of this in the last ten years I've been doing instrument programs. If you can find a...
I get a lot of "short window" void times. That's why I'm usually run-up and at the hold-short line when I make the call to ATC (no tower or GCO, so I use my cell phone).
GPS may be used as a legal substitute for DME and an NDB (fix). GPS is not approved as a substitute for VOR (even if is may be more accurate, but this is debatable). The only case where GPS may be used as the primary means of navigation on a non-GPS approach, is where there is a published GPS...
No real pitfalls. Take him/her on a flight. Observe his/her flying skills. Remediate him/her on the appropriate task(s). Put him through you own version of a mock checkride. If he/she does well, sign off. The part I don't understand is how he/she managed to fail the oral. Remember that...
Rock science this is not. He should have flown his clearance. Is there anyone here whose CFII told a student to do WETF he wanted to do instead of the clearance he got from ATC? I think not. It's all on him. Read back the clearance, get your release, depart, and contact departure.