How do you figure? The screen costs Apple roughly $200. So they don't have to hire skilled technicians, they replace the whole top of the laptop, so some backlight, cover, wiring, case...still well under $500.
The actual reason is they don't want Macbook components floating around on the grey market, so they make the pricing for significant repairs impossible to justify.
I wonder if the actual mission of their "repair" shops is to boost purchases from pigeons who have self-identified as maybe needing a new one. Repair is not at all in Apple's interest. It's certainly not for customer goodwill.
The actual reason is they don't want Macbook components floating around on the grey market, so they make the pricing for significant repairs impossible to justify.