It may be technical limitation due to heat radiated from CPU, as the GPU in basicly on the same die. It is extremely hard to make this kind of processor as there are many thing that need to be done. How Intel puled it off then? Because they used interconnect called EMIB that connects mulitple DIEs for very low cost. You cold connect ANYTHING within reasonable expectations. Example: FPGA with HBM, CPU with GPU(as in NUC).