Compile times ?
Flexibility over the backend ?<p>That would be my hunch. I think it makes a lot of sense.
Also, note that there is that project which exists :
<a href="http:&#x2F;&#x2F;llvm.org&#x2F;viewvc&#x2F;llvm-project&#x2F;llgo&#x2F;" rel="nofollow">http:&#x2F;&#x2F;llvm.org&#x2F;viewvc&#x2F;llvm-project&#x2F;llgo&#x2F;</a>