"MTR alone can greatly increase the use of NFC payments in general but for whoever reason, they want to protect Octopus."
"Whatever reason" is probably the fact that MTR/KCR own 79.5 percent of Octopus.
Corporate Structure - Octopus Hong Kong
But even if MTR has no skin in OCL, acceptance of Apple Pay/Google Pay/Paywave/Contactless will either mean all fares will rise, or pax using Contactless will have to be surcharged.