There's more to it than just investing in the Academy, Wire have done that for years, their problem is they wont give most of the young lads a chance to establish themselves into the first team. They're so desperate for instant success they quickly bin off their youngsters and buy in from other clubs.
Saints & Wigan operate differently, they promote first and then buy in when they don't have their own youngsters to take the place of players who leave. Wire just see most of their youngsters as a temporary solution to fill in for injuries and buying is always their first option.
Over a quarter of a century of SL now has clearly shown which is the best system to operate if you want to consistently win titles !
Maybe one day Wire will learn (then again maybe not )