But if you're starting from scratch, you've lost all the "little fixes" that go into making a car good.
This is also the reason massive software rewrites often fail; you rebuild the general gist quite fast, nice code, lovely interfaces etc but it will have a trillion bugs which come from decades of adding an exception here, adding one there etc. So now you have a beautiful albeit worthless product. And often these get scrapped: I know of some tax system rewrites from mainframe to modern code that costed 10s of millions and were scrapped, multiple times for this reason.
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This is also the reason massive software rewrites often fail; you rebuild the general gist quite fast, nice code, lovely interfaces etc but it will have a trillion bugs which come from decades of adding an exception here, adding one there etc. So now you have a beautiful albeit worthless product. And often these get scrapped: I know of some tax system rewrites from mainframe to modern code that costed 10s of millions and were scrapped, multiple times for this reason.
Joel Spolsky has an excellent writeup on this principle, explaining why it led to Netscape dying: https://www.joelonsoftware.com/2000/04/06/things-you-should-...
The VA has wasted hundreds of millions of dollars trying to rewrite their antiquated software.