Engines are actually changed fairly frequently because they're a wear component on most airplanes. They are also sometimes updated to a newer version or even an entirely different manufacturer. And often it's faster and cheaper to swap in a new engine that's ready to go rather than wait for the one that's attached to be overhauled, so the same engine might see service on multiple airframes.
Most cars don't operate for >12 hours a day every day. Last time I randomly checked the flight history of a Ryanair 737 on flightradar24, it had spent over 18 and a half of the previous 24 hours airborne.
And many commercial airliners are sold without engines at all.
The operators, such as Delta, do not actually own engines on the aircraft they fly, even though they own the aircraft. The engines are rented from e.g. Pratt & Whitney along with a maintenance contract. That said, that engines are in fact installed at the factory.
It’s a requirement that the airframe and engines are sold separately dating back to the original reason why United Airlines was named.
Which is not to say that commercial jets can take any old engine. Even something like this 767 that was split between GE and P&W have specific structures related to the original engine.
