I suspect this is to put a social blocker against 'elitism'. It kinds of makes the people who rush and expect you to "know all the fights" and "be geared" look like jerks, when this format is clearly designed for levelers, and random in nature.

Splitting that apart from the other dungeons in terms of format gives a space for each crowd. If you want experts who are geared and ready to steamroll a place, you queue into the other formats. If you are open to accepting/helping new players that might hit all the wrong keybinds, you do the leveling one.

Though I am surprised - if I read the original post right... is there no ability at all to even enter a leveling dungeon with a premade group? such as a guild run? I've only just returned the game about a week ago and I've just been spamming random queues to 'L2P' again... Before I left I remember doing the lowbie dungeons in guild groups all the time - is that gone now? Or can it still be done by selecting a specific dungeon rather than random?