There are quite a lot of reasons why clubs don't compete. Competing actually takes a lot of time away from training, so getting competition ready can take 6-8 weeks out of a training schedule. If the girls are older they may simply decide to skip this year, and train for a higher level next year.
F&v comps are a great introduction to competition, it's often a simple vault and a string of skills, which can be taught and polished in a couple of sessions.
You also have to factor in the financial factors for a club in competition. For each session they are competing in, they have to provide at least one coach, usually minimum level 2, often with a first aid cert. Sometimes they are required to provide a judge too. Considering weekends are often busy in the gym it can affect the day to day club running. If they only have a couple of girls in each session, which is easily done if they split by age, it can be difficult to find staff.