We camp at least once per month, + high adventure, + summer camp.
Most troop campouts are to work on merit badge requirements and rank progression. We have a year long schedule of basically what is worked on, and when, to cover everyones needs, and cover the needs of the younger scouts too.
The reason we can get a high participation rate for regular campouts, is because it is trouble free on parents part. Drop child off on Friday evening, come back pick them up on sunday. This works slick and easy when you keep gear and patrol boxes in two large enclosed trailers. They are just hooked up and pulled to a scout reservation with minimal fuss. Even that "minimal" fuss is still a pretty big deal for some folks that volunteer their time to make it happen.
Throw in that there are higher numbers of 10 , 11, and 12 year old scouts due to attrition than the older ones, and group dynamics dont lend well toward frequent backpacking. Because boy scouts are boy-led, the older boys must be there to teach the younger ones too, and get their requirements for leadership, etc.
Any one is free to get up a group of older boys to take a hike at any time. Not many adults will volunteer for that on their own. Regulations also make any small official functions a pain. Much easier for a couple of dads to just get together and take their own kids. Very difficult to match schedules of anyone up for even a weekend when school and sports are going on. Basically you are left with spring break, thanksgiving, and summer. At most summer camps you cant do high adventure treks until 13 anyway, 14 at some, so most kids under 13 are still working on merit badges to get those out of the way if they want to make Eagle, so that they can do high adventure at summer camp the next few yrs.
In the past we have tried to have a thanksgiving break campout somewhere where the rest of the kids can car-camp, and the older ones can take a multi day backpacking trip. The rule is 13 yo, or 12 if your father accompanies you and takes responsibility for your.
When they get 13 and are interested in Philmont or etc the next summer, then they start taking the shakedown hikes with their crew, so they will get three of those in a year leading up to Philmont.