Sure: Generating good diagnostics requires a large quantity of infrastructure, much of which is inherent to the compiler's design and not something readily port

Sure: Generating good diagnostics requires a large quantity of infrastructure, much of which is inherent to the compiler's design and not something readily ported piecemeal. That's not to say one compiler won't learn and benefit from changes in the other, but reimplementing features in a very different design is more than a simple "copy".