Why the DMD Backend?

[Xinok via Digitalmars-d-learn]

Given that we have GDC with the GCC backend and LDC with the LLVM 
backend, what are the benefits of keeping the DMD compiler 
backend? It seems to me that GCC and LLVM are far more developed 
and better supported by their respective communities. They have 
superior optimizers and are better equipped for migrating D to 
new platforms. On the other hand, from what I gather, there's 
lots of work to be done on DMD on improving support for x64 
Windows and ARM.

It's a genuine question, which is why I posted this to D.learn. I 
don't follow development on the backend and overall I'm 
unfamiliar with compilers, so I'm not sure what the benefits are 
of the D community continuing to maintain it's own backend.