They cost too much.
Teams know they need some low cost studs, and a bunch of lottery tickets has a better chance than no tickets at creating some cheap stars.
I'm not downplaying the importance of FAs and spending to fill gaps, but the 2004, 2007 and 2018 championships were built almost entirely from the farm of by trading top farm pieces for studs.
Yes, JD Martinez, Vic, Lackey and Manny were essential, but without strong farms, we have zero rings in my lifetime.
We sucked for decades. The same decades are farm sucked.
We came close only when we had guys like Rice, Lynn, Evans and Fisk in the 70's and Clemens, Boggs and other later on.