Having the talent as a kid is only part of the battle. Being drafted to a strong environment that allows a player to grow and develop properly is also a huge part of it and Carlton were far from that, let alone the OOFTIT's afterwards. SPS talent has been squandered and he has not developed well at all, in fact regressing as a player since his first season or two.
It's like when RL took over the side and Luke McPharlin stopped flying for marks and players were hesitant to go forward and attack with the football, even Stephen Hill was stopping and looking backwards first instead of playing on his natural attacking instinct. Your playing and training environment is a massive part of how you develop as a player.