My understanding is that they needed to to do this because one of the main chips, the video chip, is no longer available, and since they were using FPGA for tha

My understanding is that they needed to to do this because one of the main chips, the video chip, is no longer available, and since they were using FPGA for that, I assume at that point the cost is driven down by just implementing Z80 in there too, with little loss of quality.