In Australia - Telstra, Optus, and Vodafone maintain their own independent mobile networks & equipment (Telstra having the most coverage in rural areas).
If the author used 3 MVNOs from the same network, then it'd be silly.
Telstra, Optus, and Vodafone might share the same physical tower though (while using different antennas and RRUs). But that's only an issue if there are severe interference issues there (on all the bands the author is connecting to) or if the tower itself suffers some catastrophic damage.
If the author used 3 MVNOs from the same network, then it'd be silly.