The question is more about "how much" of PD they support right? Like PD has standards for charging at higher or lower currents.
My understanding of the current-gen MacBook Pro is that they support some kind of "fast charging", but only if you use their MagSafe port. You can still charge on the USB-C ports, but not as fast as you could with MagSafe. I'm not sure if that's a violation of the regulations, or if PD simply doesn't have support for the amount of power they're pushing through the MagSafe.
But I think the point is that they'll continue to look for ways to offer a better experience with their proprietary stuff, even if they're forced to support a standard in addition.