Yes, it's very silly...
The reason it happens is because the GPS receiver is in the cellular baseband chip, and when you put an iOS device into airplane mode, Apple power down that whole chip.
t's just that with the iPhone you can't disable the phone without disabling the GPS unlike some Android phones.
So, in order to reduce costs they chose a chip design, where the mobile part and the GPS part are on one chip set
Actually, that's all a load of nonsense.
Just checked on my iPhone. Airplane mode on, location services on .... can still see my location on a map.
Maybe you're confusing yourself by trying to use maps that are not stored on the device but require an internet connection to download (those will need either cellular
or wifi to be turned on, obviously !).
P.S. ChickenHouse ....even if what you said were technically correct, its not about "reducing costs" ....its more like efficient circuit design, reducing the prospect of chip failure
AND reducing power consumption.