It's the leader's fault almost every time.
This is an observation of every single trial, task force or raid team I have ever been a part of... but other than Master Of runs, it usually doesn't matter as you're still going to finish even though leaders are making this pretty significant mistake.
The end game content is almost ALL new to me. Sometimes when I'm on these, it's the very first time I've done the trial, let alone tried to do it in a specific way. The leaders of these are typically so well versed in the trial that they take for granted how little people know about it. In fact, many of the people joining your trials might not even know what "master of..." means or why anyone wants it. They may not even know that things they do keep the entire team from getting the badge. This is hard for people who are very competent and knowledgeable to wrap their brain around but it is common in nearly every field. The more advanced you are in a skill or subject, the further your perspective shifts away from the beginner's... until you become an experienced teacher of that discipline.
People like to be told WHY they are doing something. If we are not supposed to kill a certain person, or if we are supposed to stay in a certain area... it helps to be told why. "If anyone leaves this spot, we won't get credit for X." is a pretty simple way to cover things like this. If you're confused by this because "Duh... everyone knows why we're doing this" then you need to go back to the previous paragraph. People still might run ahead or lag behind or do the wrong thing, but I bet you would see a significant increase in compliance if you were just more thorough in your explanations instead of just assuming everyone already knows the play.