CTCs pass rate from online application to people who start in NZ is about 2-3%.
OATs assessment has about a 50-60% pass rate, as has been said it is true they are very much a business and so can't be quite a selective about their pupils, but this is not all that they have to consider. Since they are a business people can decide to come to them or not and as such they have to make sure that they don't do anything to affect their image. The last thing OAT wants to do is to accept lots of totally unsuitable people to the course. While yes this would get them lots of money it would also mean that the failure rate would significantly increase and would most likely affect the image.
I've just started on OATs APP and so far I've been impressed, all the instructors are very switched on and the lessons have been a pleasure not a chore.