yup, because the tools in the drawers of your roll-away have nuances you have to learn - a syntax if you will. And each of the potentially bad parts you need to replace has interactions with other parts of the car (the system).

I just changed the alternator on my truck - you have to wait for the exhaust to cool before you do it, disconnect the battery and then punch the security code into the radio when you're done.

A business person trying to write their own software (assuming they're not also a developer and that they believe some magic tool will let them complete it) will end up with painfully burned hands in the process and at the end they won't be blissfully listening to music again.