My guess is that the implementation is not good enough, and fast charging generates a lot of heat in the handset. Only with their own charging can they guarante

My guess is that the implementation is not good enough, and fast charging generates a lot of heat in the handset. Only with their own charging can they guarantee enough heat dispersion in the charger. Wireless charging is a bit lossy and can generate a lot of heat - I know this from experience designing devices, although everything else is guesswork. Whether it was always intended to be incompatible,or they had to put the hacky handshake in late in the process to prevent the device being 'a bit fiery' I don't know.