For the other networks, you’re probably seeing RX1 for SF11 and SF12 then? Selecting RX1 or RX2 is up to the provider.
Thinking about it, I wonder why TTN prefers RX2 for an OTAA Join Request in SF11 and 12.
(It’s understandable for regular downlinks that are responses to uplinks using a high SF, as then, for RX2, TTN uses SF9 with a higher output power, where the lower SF9 limits the valuable airtime, and limits the time that the half-duplex gateways are “deaf” while transmitting a downlink. But for a Join Response, it needs to use the LoRaWAN defaults anyhow, for which RX2 does not seem to have much advantage over RX1, at least not for EU868? Or maybe the duty cycle is better for RX2?)