Because some clubs have advantages over others, and the same old teams winning it year in and year out makes for a boring competition. And the AFL do it successfully with the draft. Note Brisbane leading the AFL.
Drafts are bad for sport. It promotes mediocrity and punishes success. Might as well hand out certificates for participating every year.
Good kids are forced to enter bad environments and it stunts their development. Melbourne, Carlton and Gold Coast are all proof that the draft system doesn't work if the club is broken. There is no way that the Titans deserve access to the best kid in RL.
Only 3 number one picks since the AFL draft started in 1981 have gone on to win a premiership at the club that drafted them.
Melbourne and Sydney aren't where they are because they stockpile the best kids in the game. They make them the best kids in the game.
It also creates more dead rubbers at the end of a season as clubs decide they're out of the premiership race and give up on the season. You don't get sides like Canterbury taking down top 4 contenders at this stage of the season if it means dropping down the draft list.
With a draft system, Cody Walker and Damien Cook would've most likely disappeared into the wilderness before now. Both played for NSW this year. And there are plenty of other late bloomers in the NRL that would've been missed I'm sure.
The only positive that a draft system has in the offseason is when it creates hype for a couple of the spring months. Otherwise it's very much just dictating to kids what path their career is going to take.
Clubs need to improve from within, otherwise nothing will change.