As anyone who's used Mentor Roulette can attest, the biggest problem with EX trials is people who:
1. Have no idea what they're doing.
2. Are severely undergeared, at least in terms of accessories, meaning they'll just die if they're in the wrong spot.
3. Don't talk in party chat or say chat, and don't listen to any advice given in party chat or say chat, meaning they will KEEP dying by being in the wrong spot because they're unable to take advice.
4. Never say yes to Vote Dismiss or Vote Abandon, prolonging the miserable experience for everyone involved.

The best way to fix this would be to add a warning similar to the one given for BA to the first High-End Duty that a given character queues for, if not to all High-End duties.
For example:

"The Howling Eye (Extreme) is an extremely punishing duty. Emerging triumphant will require teamwork, knowledge, and especially willingness to listen to advice. Failure to have these will make it impossible to clear."