First off I'd like to point out that there are certain achievements in this game, mostly PvP related that are very difficult to achieve now because the content you get them from is dead. I am, ofc, talking about the wins in old level 50 frontline content - no one does that anymore, because people have moved on to the level 60 versions. And even there you can notice how a new version often kills the others. Now, the achievments could be easly adjusted to let every frontline-win count for example instead of making it extremly difficult to ever get them (some have tied gear, monuts and titles to them); infact its probably way more difficult to get those wins than to get any of your EX-primal clears.
So there is actually something in place thats screwing those who are late to the party.
Now, to the point I quoted here... I'll repeat again: This is a game, that everyone plays for their enjoyment. It should give us the option to actually make sure we can enjoy the content we want to do. And if enjoying it means not teaching it right now, the game should give me the option for that. I dont take that option because I dislike new players - I take this option because I want to enjoy the game I'm playing. By "forcing" me into a queue with people that simply make my game less enjoyable (without that being their fault, really) you turn this game into stressful, frustrating "work" for me. My hobby shouldnt make me do things I dont want to do. I might sound very selfish right now, and even more selfish than I am or would like to sound, but you really have to understand that asking people to do something they dont want to do (if they want to teach people, they'll queue for that option) is bad - specially when its happening in a game.
Your fix for people not wanting to teach/help new randoms in DF is simply forcing them to do so by not allowing them to avoid an experience they dont want to make. Thats really not a good solution - specially not when it involves taking away the option they previously had to make sure they could play the game the way they wanted.
A new players person experience and enjoyment of the game is NOT more important than that of a person who has been here since 1.0. Their first clear is not more important than my 99th that will give me the token to get my bird - their first clear is ofc very important to them, as is the token very important to me.
Both sides need to be emphatic (...okay, that word seems wrong, if someone can suggest a better one, I would be thankful - not native, sorry >.<) here and have an understanding for the wishes of the other side. You are basically saying to everyone who has cleared the fight yet "Well, yeah, to bad that you still want drops from here and be rewarded for your knowledge of the fight now - get back to square one, please, because its more important that stranger XY learns the fight too than that you get what you want now"
You are currently looking at the problem only from the side of the new person, because you decided that they are more important and that can not and should not be the case.
I totally see the problem of people not queueing for "learning" - but the solution for that problem is not to take that away from them but instead give them a better reason NOT to do that.
Besides... we really need to get rid of the idea that you can clear EX-primals in DF. The game is very missleading in my opionion when it suggests that you can just go on and queue for them solo. I dare to say that it is impossible for a party of 8 random people to get a clear of any EX-primals when they all go in blind - those fights take more than 60 minutes to be understood and learned. By just letting you queue for them like you're used to from dungeons (all CAN easly be cleared within thegiven timeframe of 90 minutes, even with everyone going in blind) the game is giving you false hope and a wrong idea of this content.