It used to turn them off on the iPhone, but not these days.
A lot of planes have WiFi, and people are also using Bluetooth headphones. So when talking about being a passenger on an airplane, this seems like a rather practical choice.
Not for my Android phone, at least not by default (Pixel 9a a/ GrapheneOS). It leaves Bluetooth and WiFi on in airplane mode. I doubt this is specific to GrapheneOS and may say more about AOSP.
Not if you were connected to either when turning on airplane mode. Both can also be turned on manually in airplane mode. A physical block avoids any uncertainty or mistakes.
A lot of planes have WiFi, and people are also using Bluetooth headphones. So when talking about being a passenger on an airplane, this seems like a rather practical choice.