FPGAs are pretty bad space-wise and power-wise compared to straight up ASICs. Apple could make some blocks highly configurable, but even an FPGA designer wouldn

FPGAs are pretty bad space-wise and power-wise compared to straight up ASICs. Apple could make some blocks highly configurable, but even an FPGA designer wouldn't use FPGA fabric to do multiplication if they cared about performance. FPGAs are a mix of general purpose logic blocks (the fabric) and dedicated blocks like multipliers, dividers, PLLs, memory, serializers and deserializers, etc.