I have seen the same thing happen with individual dens in a pack; boys who seem to 'earn' every rank with very little attendance and participation, or who 'complete' every requirement for a Webelos activity pin in 30 - 45 minutes. They then move on to the troop and flounder, unable to move past the initial Scout rank in over a year. They do not seem to understand how they were able to get credit for an award in Cubs while not completing all of the requirements, but cannot do so in a troop where Mom or Dad are not the ones who sign off on requirements.
While I can understand that a Den Leader may not want a child to 'stand out' by not being called up with the rest of the boys for rank advancement, that is far better in the long run than having that Scout quit a year later because he is no longer being automatically recognized with everyone else.
One of the things we now do to help alleviate the issue of 'everyone got their rank tonight except me', is to award that rank at the next Pack meeting after it is earned, rather than a mass award at the end of the year. When they are all called up at the same time, everyone notices the boy whose name is not called for advancement. When rank is awarded as soon as earned, that does not happen.