That's because you can not install Yosemite on your "recovery" disk. First of all, it's too small to hold Yosemite and secondly, it contains your recovery utilities which without you would be unable to do disk checks or reinstall Yosemite if need be.
Shop for your Apple, Mac, iPhone and other computer products on Amazon.
We are a participant in the Amazon Services LLC Associates Program, an affiliate program designed to provide a means for us to earn fees by linking to Amazon and affiliated sites.