Actually the theory is MLS clubs develop players through their academies in order to sign them to Homegrown contracts. Homegrown contracts don't count toward the club's salary cap. There's also the potential to make money off a transfer fee to foreign clubs.
The problem is with the exception of Dallas FC most MLS clubs have failed to develop players that attract foreign interest or even become MLS first-team caliber. In Europe, a graduating academy class will usually output 3-4 professionals every year. Usually at least two of those will be a starter somewhere within a couple of years. Whereas the MLS has a dreadful track record of Academy players becoming first team players. Right now Academies are basically a feeder system for College soccer. Then after a year or two, you might have some players come out of it and end up even further behind when they get signed to an MLS team.
Dallas FC is the only academy that actually uses it as its intended purpose. The rest just use it as a marketing tool or treat it as a mandatory operating cost. LA Galaxy is an odd one. In some ways, they've made some real investments into their academy and USL team. But there seems to be a disconnect between how their academy/USL players fit into their actual strategy with the LA Galaxy first team. It's partly due to LA Galaxy being capable and almost expected to attract a big name aging Euro-star. LA is about star power and hollywood, so developing players slowly from the groundup may not necessarily fit with the marketing objectives for a big market team. Big clubs in England like Chelsea and Manchester City run into similar problems. The difference is their academy players can still get professional contracts elsewhere. The Galaxy academy players end up in obscurity.
That said, the new Galaxy coach who took over from Bruce Arena has definitely taken steps to integrate more of the LAGII players into the first team. McBean has been getting a lot of field time lately, and even Virirael and Ari Lassiter have gotten some first team minutes already this season. The new Galaxy coach was the former LAGII, so it's not surprise he's brought along some of his favorites, but it's still a step in the right direction.
Whether by proper organization or just dumb luck, one of these MLS academies will eventually develop a player of near Pulisic's ability and market value, and then we'll start seeing other MLS academies seeing the value of developing and grooming homegrown players. Pulisic's estimated market value will be around $25 million fairly soon. A single transfer fee of that amount would pay for the Galaxy academy for the next 6 years...
