Yeah it is I see shout groups all the time doing this
1) Not all of those shout groups happen
2) you're right, it's not the same people doing it; that's what makes it so hard. You might get lucky and get one group that pops it once one day, some other group that pops it next week, yada yada. More often than not the people running it want what you want, thus you can't have it. The only likely exception is if you're doing staff, because no other weapon shares the same trial NM and nobody wants it.

It is not a simple matter. Just because you see people shouting for one of several different NMs here and tehre does not mean it's easy to join them AND get what you want.

When you're soloing/duoing with a friend, you have control over when you do stuff and you dont have competition. The unpopularity of WoE makes that even less of a problem. And again, with WoE, it's only one difficult, time consuming trial, not three (And if by some stroke of luck you DO have a group to do it with, you can probably get all three trials done in a day)