Here is the post you were most likely referencing, from earlier in this thread:
The last section of his post is pretty important - 'because he was not listening.' Often times, the people I have personally ran across who did not have their job crystal soon after reaching 30 were either uninformed (happens) or more often straight up did not care. They are the types of players where the other people running around are little more than mobile npcs to them - we're all supporting actors in the play that is their game. They don't care if they waste someone else's time, but there is hell to pay if someone wastes theirs. They don't care that running as a Marauder instead of a Paladin gives you significantly fewer tools and means to perform your role effectively; etc.
It's those people - the people who are so far down IDGAF Boulevard that grouping with them is going to be at BEST, something you slog through... Because of those people, yes minimum requirements would benefit the vast majority of players. Realistically, it wouldn't adversely affect a lot of people. Maybe someone who JUST hit 30 and wants to jump into an msq dungeon to continue the story might be a little irritated they would need to go do other stuff first. I know I'm guilty of doing a lot of the SB job quests once I hit 70, because I have gear waiting on the job for when it maxes. Some of the solo duties in the 60s were pretty rough if you were a little behind in gear.
But as someone who personally went through a portion of Qarn a few weeks ago with a 30 something Conjuror who didn't have their job stone and was unable to keep the tank alive...so they bailed and we had to sit and wait on a replacement midway through... That was a bad run for 3 people because it. Same went for when I went through B. Wall with a tank that was very poorly equipped. Super nice guy, was there only to help, but his lack of gear was too much for the healer to handle. So he stepped aside after saying repeatedly he had bad gear, and we had to wait for a replacement. Someone even put it in the Tales from Duty Finder a while back.
Just my thoughts and experiences.