Large MoE models are too heavily bottlenecked on typical discrete GPUs. You end up pushing just a few common/non-shared layers to GPU and running the MoE part on CPU, because the bandwidth of PCIe transfers to a discrete GPU is a killer bottleneck. Platforms with reasonable amounts of unified memory are more balanced despite the lower VRAM bandwidth, and can more easily run even larger models by streaming inactive weights from SSD (though this quickly becomes overkill as you get increasingly bottlenecked by storage bandwidth: you'd be better off then with a plain HEDT accessing lots of fast storage in parallel via abundant PCIe lanes).