Google Voice and Project fi Not Sitting in a Tree

I love Android. I love Project fi. And for a long time (a long time ago) I loved Google Voice. Then Google Voice languished for 5 years. Then out of nowhere Google announced renewed investment in the service.

But if you use Project fi and you try to log into Google Voice you see this error.

Can't even log into Google Voice if you use Project fi

Why Project fi and Google Voice can’t share some of their sweet functionality is beyond me. Though I suppose I shouldn’t be completely surprised considering this is the company that has, as of the time of this writing, no less than four different messaging apps.