This. Even resin printers only get you kind of in the neighborhood of tolerance. Lego primarily uses injection molding for their parts. Their molds are insanely tight and low tolerance. One of the key costs of Lego bricks is the lifecycle of the molds. They don't last forever and lose tolerance over the course of several hundred thousand injections. Managing these molds and the sheer variety of parts they produce borders on logistical insanity. It is one of the most impressive logistics operations on the planet. I can build a functional car with fewer discrete pieces than large modern lego sets.