what if you get a chance to steal it but can't
Chinooks are considered advanced aircrafts that are incredibly hard to fly, which is why you have to be special forces pilots to fly them IRL. Your argument is seen and rejected.
The same can be said for a bunch of equipment in the game if we look at it through that lens. The only time it really makes sense to lock gear behind challenges really is just event stuff which is often cosmetic, or Phantom Program which is ofc a hyper elaborate easter egg and is ultimately a loadout item not this large vehicle that will take up a ton of space on a map and be effectively a paperweight for most of the server.
Nothing would prevent you from getting into a friendly one to shoot its side or rear guns. Hell, one could even argue you can't get into someone else's mortar, since that's classed as a vehicle, so there Is no rationale behind "should be able to steal a hostile one" childlike entitlement just the same as you cannot do it with the Traverser/LTV
