The only thing I can think of is that the Gateway does need to measure the solar inverter current, so a pair of Current Transformers (CTs) will need to run to wherever they can get to clamp over the AC lines that run between your inverter(s) and whichever panel they tie into. I don't know what Tesla's limit would be for how long the Gateway CT wiring can run, hopefully that's pretty long, but they are sensitive low-voltage devices so there might be a point where if it's too long the signal is lost, or less accurate, or too susceptible to noise to work properly. I guess there practically has to be a limit to the length of the wiring that connects the Powerwalls to the Gateway also, though since that's RS485 as I understand it, that should be able to use quite long wires. I'm pretty sure the CTs would hit their limit before RS485 does.
I see the Neurio (what's used to read the CTs inside the Gateway) manual says it has to be within 4' (that's the length of the provided CTs), but I know Tesla does runs longer than this (mine might actually be 4', or perhaps 6/8'). I did find an extension on the web (Neurio CTE-10) that says not to extend beyond 50'. And of course that would be distance through the conduit, not straight-line.