Orbi - why can't we change channels on satellites?

That is how ORDINARY repeaters and extenders work. But the Orbi is not an extender or repeater. It is a mesh network with a dedicated backhaul link, effectively operating as if each AP had a wired connection back to a switch or wireless controller.

In a mesh network, unless the APs are optimally placed with sufficient separation to eliminate co-channel interference, there will be problems. This is almost never possible in a typical house. The only advantage of having the same channel is to avoid latency when a moving device changes channels/ap links. And I am not sure if latency is actually eliminated when AP placement is not optimal. For example, I have one unit on the first floor and one unit on the second floor - directly above the other. Because I want physical ports in those locations.