When I was a new player I found it odd to never get into a dungeon in progress, but to be fair, [in my experience] people leave mid run so rarely that I just thought nothing of it. Doesn't help I came from WoW where people leave left and right so I thought it was just a different type of crowd, idk. Imagine my surprise after finding out you can actually toggle that feature on and off, now all the times I saw 'DPS in need' and yet get a 20 min queue makes so much sense!