The companies know they're skating near the thin ice.
In this case, one of the terms of the MAP agreement is that the retailer is not to let anyone know about the MAP policy. It's absolutely secret.
The most obvious explanation for not displaying the price would be a statement such as, "our prices are so far below the manufacturer's minimum advertised price policy that we can't show them. Click on the Add to Cart Button to view our price."
That would make the manufacturer look bad, though. Thus the secrecy.