The bit you’ve missed out here is that the ARM64 ISA is very different to earlier Arm ISAs and that Apple almost certainly was deeply involved in its development and was first with a production core.
Given that and in the absence of a clear rationale I find it hard to see why Apple would want to to incur the costs of a move to an ISA it’s had no influence over - certainly not to save an immaterial licensing fee.
Given that and in the absence of a clear rationale I find it hard to see why Apple would want to to incur the costs of a move to an ISA it’s had no influence over - certainly not to save an immaterial licensing fee.