... You mean I'm not going to be the CDS in 10 years? Dang, there goes that plan!
Anyways, being found suitable and getting selected are two different things. Depending upon the trade in question, there may be more people who are applying and have been found suitable than there are spots available at this time. In that case, you not only have to be a "suitable" candidate, you need to be more "suitable" than all but X - 1 other candidates, where X is the number of spots open.
For some trades, there may be either a very limited intake due to lack of training slots, or a simple lack of demand for personnel, and for other trades, there may be sufficient spots available that everyone who is found "suitable" in that fiscal year is able to enrol as that trade.