The tricky part isn't the protocol, it's all of the interfaces with weirdo hardware clocks. Even just parsing GPGGA messages from a serial port can be tricky when you're trying to keep the timing tight.
There is immense value in replacing simple NTP deployments, which don't interface with weirdo hardware clocks, with a memory-safe alternative; those simple deployments dwarf the weird ones. It is fine (good, even) for there to be multiple viable implementations of NTP, fit for different purposes.