For those of you not familiar with the Cub Scout program, this is kind of how it's supposed to be set up.
For boys in 1st through 5th grade, groups of 5-8 boys in a grade level are called a den. Each den should have a leader and assistant leader (2 adults). In the 1st grade year, the boys are called Tigers and are required to have their adult partner attend meetings and events with them. Sometimes adults in that first year take turns leading the meetings and planning the trips for their den rather than having a single leader. Meetings would occur 2-3 times a month. For each grade level, there is a handbook with requirements and electives appropriate for that age- and often times a theme would build upon itself in subsequent books- like outdoor skills or emergency preparedness or family fun. Another option is for the boys to earn belt loops on a specific topic and these are able to be earned through the entire cub scout program no matter what grade the boy is.
All the dens come together once a month for a Pack meeting. This is where the boys receive awards, show off new skills or projects, and have some fun- often with a theme. The dens may also prepare skits or songs or whatever to share with the pack. This meeting is headed by a Cubmaster (who isn't supposed to be a den leader, but sometimes acts as one anyway).
Then there is usually one meeting a month for just the adults in the pack to keep the pack running a good program. This would be organized and led by a Committee Chair (who is not supposed to be a den leader). The pack should also have a Secretary and Treasurer just like any other organization, however, there is no restriction on who can do that job. It's also good to have one person from the pack (anyone) to be in charge of advancement and awards- to make sure all den leaders are on track for boys earning ranks- to make sure all boys are getting recognition at pack meetings- to make sure den leaders input the pins/patches that need ordered- to purchase and sort the awards for the pack meeting. It's also good for one person to be in charge of promoting day and resident camps- collecting forms and money- and making reservations for activities/programs/camps since they are often open to multiple den levels at the same time.
And each pack needs to have an adult who is a representative from the Charter Organization who would take care of any issues between the pack and the place that sponsors a pack.
So, besides the charter org representative and the supposed limit on number of kids in a den... a Pack would run just like a Girl Scout Service Unit with each troop being kind of like a den and all the dens coming together from time to time for an activity and the Service Unit leader would be like the Committee Chair. If you think of it like that, you can see why it demands more adults. A Cub Scout Pack is set up in a way that support and assistance for new leaders/groups is built into the program and so that a single leader (like in Girl Scouts) would not be entirely responsible for everything from programming to financial stuff to events to awards to opportunities for multiple ages interacting. When our pack had more kids, we had more adults and it was running more or less like this says. It was very nice having others to work with and to take the pressure off me for some parts of making the boys stuff work. With Girl Scouts, I know it falls completely on my shoulders to make the troop go, plus I have to do more with the Service Unit to make the interactions happen as well.
If I've left anything out or you can explain something better- please feel free to add it here.