I don't think it's the throughput, but the variance. There are so many places for something to go wrong between two computers, so doing something that needs a very tight latency budget is hard. Harder still when you don't have control over any of the parts connecting things. In a DC, everything can be built for qos and latency, but on a desktop you're using a porbably garbage router with a home OS running a million things.

I actually found the lag and compression artifacts between my Mac and gaming PC (which are connected by cable to the same switch) using the Steam remote play thing to be actually worse than Stadia.