I have noticed some gyms don't focus on take downs, unless they have a special comp training class. The kids classes always start on their knees.
I trust that different gyms have different training strategies and so know that they would be doing this for a reason.
Why is it that some gyms don't focus on take downs and doesn't this affect comp performance?
BJJ clubs often don't work takedowns because they regard stand-up work as more dangerous. This is not unreasonable. Even many judo schools will have prepubescent students practice more groundwork than throws.
In particular, takedowns require students to pay attention to when they might get thrown, and execute a safe breakfall when they do. Being able to break a fall from many positions is a fairly complex motor skill that takes time to develop. Small children, especially those that are only training a couple times a week, often have quite poor breakfalling skills for years into their training.
There's a lot of curriculum to teach in BJJ: open guard, closed guard, mount, side control, back control, all of those positions in reverse, plus triangles, armbars, Kimuras, Americanas, naked chokes, and gi chokes. In contrast, a student doesn't necessarily need to learn throws in order to win--they can pull guard or get the fight to the ground by just...kind of...figuring it out....sometimes. (This approach favors the naturally athletic and aggressive and I therefore don't favor it.) Since kids have a lot of groundwork material that they absolutely will need to use, and the throwing material is not necessary to win in competition, a lot of instructors will leave it as an advanced topic.
Students who don't know takedowns, or who have only done a class or two on them, will have to pull guard or rely on innate wrestling ability. This dramatically reduces one's options in competition, and leaves the student open to being dominated in the important first seconds of any match.
I don't BJJ; however, I do karate and Judo and I agree with reasons previously provided.
When I teach Judo, we know the break falls and have good quality mats so throws are executed. Even then, we don't always perform full competition strength throws so that everyone can remain safe and we can continue to train.
When I do my karate class, I am even more careful. The quality of the mats aren't as good. Along with that, the kids work break falls and are thrown a lot less - as a result, safety becomes a bigger issue. And also, the focus of the class is not to do that. I am actually planning a mini-Judo lesson for my beginner karate class and instead of being a standard Judo class it will focus more on break falls, defense to get to standing again, and one or two basic throws.
As for competition, training or lack there of in specific area will always affect how you perform. Also, the rules and tournament system will also change how you perform, i.e. Judo vs. BJJ competitions.
To add one more point of information, it might strictly be a matter of insurance. I'm able to offer martial arts classes at work, but their insurance specifically forbids takedowns and free-sparring unless you have certain certifications. Frankly, it's an arbitrary rule, but it's one that us teachers have to hold to because that's how the agreement is phrased.
