I don’t know why people think this. USB-C is on every Apple product except iPhone and AirPods, and they were quite an early adopter of it, putting it on the MacBook in 2015. For comparison, the first Samsung phone with USB-C was the Note 7, 1.5 years later.
They’ve done nothing proprietary with it in all that time, and Apple products with USB-C have followed the spec quite closely (unlike offenders such as Nintendo). Outside of unsubstantiated rumours and FUD, there’s no reason to think they’ll do anything different.