Honestly that's not how it works any more, it's not just a Tigers thing.
Top-tier junior talent has a huge bargaining chip for any club who is short in a particular position, and can earn top dollar by moving around. Loyalty is a very distant consideration.
And when half of all the best juniors don't become successful career players anyway, it's in their best interests to secure big early (perhaps desperate) deals before they've truly been tested at the top level.
E.g. Schuster, who had junior raps on him as good as any big 5/8th cum backrower has had in the last 20 years. Used that pedigree to secure a big last junior deal from Manly, then his first adult contract also on big dollars, leveraging other clubs interest to max out the deal.
Fast forward 2 seasons and he's cooked and Manly are on the hook for a big value 4-year deal for a bloke that cannot maintain a decent output. And he was tearing the juniors to shreds when he played kids half his size who could not tackle.
But Schuster would be doing just fine, he's been paid a few million by Manly for about 40 average matches and about 10 good ones.
And not to forget the manager's cut on each transaction. It's a real feeding frenzy at the junior level.