They have a chance to get queued together with people who want to learn/help in the duty incomplete queue. Of course there will be much less people who are helping new players to clear the fight, compared to people who just want to farm the fight. As I've said multiple times, sometimes helping others learn the fight means not clearing the fight itself, which means you earn nothing from spending 60-90 minutes with them, other than the pleasure of helping others and helping the playerbase get better as a whole (which admittedly, doesn't help much to get your bird mount or weapons/tokens/whatever).
There's a queue for aim to clear group (duty completion + duty incomplete). You make it sound like it's impossible to clear the fight together with others who haven't clear too. It's hard but doable. I did it in thordan ex, which arguably is the hardest ex trial in heavensward, just by joining practice/clear PF groups. Some of these fights are hard enough that you won't clear even if you're the only person in the group who haven't cleared. If you're late to the content it'll obviously be harder for you to find people to learn and clear the fight together, but that's just how it works in this game. You can't really avoid obsolescence in a vertical progression MMO.
Let's go further and think about the reason why most cleared people only want to go with people who have cleared too. The answer is quite simple, because the content is difficult enough. It's hard to carry people who know little to nothing about the fight. It takes a very long time to completely teach them the fight. You can probably slip into a ravana or bismarck clear party with bonus, and people will just ignore you and clear the fight while pretending you never existed, because they still can. That fight is so easy due to overgearing that you don't see half of the whole fight. It's a different problem if you slip into a12s queue without knowing anything, and if I was going to farm a12s then I'll definitely have problem with it since that pretty much means it's impossible to clear it. It takes hours (even weeks/months) for people to learn a12s before they clear it. When I join a practice or clear party for a12s I do so while keeping in mind that I don't expect a clear, but when I farm of course I expect clears (preferably smooth and easy ones too).