CBCT is for detection of phae imbalance between two phase, now imagine phase to phase foult current increase at higher level but remain in balance phase different (120 for most) thats why it cant detect phase to phase foult.
It’s not designed to.
A phase-phase short will trigger overcurrent protection, which will be much faster.
Balance techniques are not always arranged as a fatal trip. In some circuit configurations they can be thought of as an alarm, rather than a reason to interrupt service.
CBCT is an extra sensor, not a substitute for standard protections.