I'm not saying with authority that it's the case here, but ...

... Some parts in these new cars (maybe including the parts about which you're inquiring) have to be installed using a dealer's VADIS computer, sort of a "handshaking" process to make a "formal introduction", so that the parts work with the rest of the car's systems, especially including the main computer.

It all depends on the model, the model year (you didn't specify), and the particular parts. E.g., in some Volvos, you even have to do this with a new power seat motor! Therefore I would expect, and if I owned such a newer car I would sincerely hope, that this especially applies to anything as critical as the starting system, viz-a-viz the potential for stealing the car.

Gone are the days (240's and older cars) when you could just bolt in anything to cobble a replacement or even just try out a suspect part. Too much government regulation (the car should operate efficiently and safely), manufacturer liability/warranty concerns, and public pressure to reduce auto theft.