Because stunts are obviously very dangerous, they're very expensive, and there are a lot of stunt scenes that you cannot do, obviously, because you can't really allow the stuntman to be seriously hurt.
потому что трюки — вещь очевидно опасная и дорогая, и потом, далеко не все трюки физически возможны, ведь нельзя допустить, чтобы каскадёр серьёзно пострадал.