Why doesn't Apple allow you to restore your photo library locally while using iCloud Photo Library?

I ran into that too. My library is 400 GB. I could either restore locally and let it upload everything, or just open fresh and let it download everything. I tried it partially both ways and wound up going with the local restore. The download seemed only to get all the thumbnails and download full files when items were viewed.

Very poor implementation. Now I've already blown through my monthly Comcast data cap for October.