Non-enforcement of the tee sheet is probably one of the biggest problems. The course has a dilemma: either cancel the group if they aren't ready (and refund their money/lose the cash) or take their money, shuffle the tee sheet around and piss folks off and slow up the course for everybody else. Most courses probably go the latter route.
I guess strict enforcement of a tee sheet works out OK. The courses that are so busy that they have to be strict probably can afford to lose a customer or two by turning them away for being late, and the courses that don't have enough customers can afford to be more flexible about strict tee times because there are empty tee time slots.
Most of the courses around here are hanging on by a thread finacially and the courses are seldom full. A group that gets turned away because someone is a few minutes late likely wouldn't be back. If they are regulars (and especially if they have lots of friends that are regulars) and they all take their games elsewhere it's a big deal. A potential pitfall to running any business in a small town is if you do something unpopular you may lose everybody.
The point being that apparently your course isn't that busy. My home complex is the busiest facility in Denver, with an 18 hole course (par 72) and two 9 hole courses (par 27 and par 31). Being a muni operated by the Foothills Recreation District, it serves as a cash cow for many of the other recreational services offered by the district. Even on a slow year, they will return as much as a 3/4 million dollar profit back into the district coffers. All 3 courses are run on a reservations system, since that's the only possible way to keep things straight with so many players passing through.
The first tee for the Executive 9 is right next to the first tee for the regulation course (they share a common cart path and the first greens on each course are only about 150 feet apart), and we have had players who paid for the 9 hole course try and slip on to the big course at the second hole. As far as I know none has ever actually been successful in getting more than halfway up the second fairway before getting caught, but that doesn't seem to stop them trying.
We work hard to keep control of the flow of players, but still seem to sometimes end up with rounds pushing 4:45 to 5 hours by midday on busy weekends.