You're on a gondola between Pop and MK, on a hot July afternoon. How far in advance of a potential thunderstorm does Disney have to be to safely shut the line down, vs. the length of time to get from Pop to MK? What happens when a storm bringing lightning and high winds pops up 5 miles off-property and moves in, which, I think, has happened a time or two in the history of the resort? It's a far cry to shut down lines that are 5-8 minutes in length vs. something 2x, 3x, or even longer than that. Now link up two dozen resorts, and have backup buses and drivers at the ready.
This topic has been brought up, discredited, beaten to death, and then resurrected and beaten like a dead horse again by the same people so many times now I've lost count. Expansion of the existing line to other parks is NOT happening.