A lot of threads here talk about them being the 'best' candidates.
But weren't they essentially all washouts? Several, if not most, of the candidates state that something is holding them back from "making it" as profilers.
shareupto that point before when they go for a drink, they were the best out of the rest. it was during drinks time that they find out who made profiler and who didn't. a couple of them didn't because as you say, something was holding them back right towards the end of their tests.
however, the island helps some of them get over it like the lady who was quite weak throughout the movie but showed her strength at the end when she got in the water and took down lucas.