The only thing useful that Fitbit has is marketshare (declining), community and maybe patents.
From my experience with their products, you do not want their experience in the wearables space ... It is not going to help to compete with Apple and Samsung.
You’re confusing the product with production. Google has plenty of product people that can tell them what to build. FitBit has engineers, hardware designers, production capabilities, suppliers, distribution, as well as the ownership of name ‘Bit’ in the wearables space. Makes perfect sense if Google is trying to make a rapid push into a new market.