They're fresh designs, just like how if 10 people reimplement the same 100 page specification, they'll have a stage of fixing crashes unique to their implementa

They're fresh designs, just like how if 10 people reimplement the same 100 page specification, they'll have a stage of fixing crashes unique to their implementation, fresh rocket designs need a few rounds of iteration to sort out all the kinks, and after a point you're just better off doing a test flight, especially as a private company. You just don't really hear about similar issues for things like cars because you don't get large fireballs and air closures indicative of testing. Once you get the issues sorted out though, they can be almost airplane like in terms of operations. See SpaceX's crazy launch cadence and reliability streak with Falcon 9 for an example.