I personally trust Google way more than Facebook (and most of my friends do as well).

Biggest factor in adoption is product perception. People associate Google with finding information. Not with playing. They associate Facebook with games and pictures. They associate Twitter with celebrities and gossip. Apple with trendy devices. It's extremely hard for any of these companies to leap into another area and break that cognitive barrier no matter how good the product is. Especially when the product is deeply connected to the existing popular product. A lot of people think integration is an advantage but only if it's integrating related things. For something totally different it's better to create a new brand.

While I don't fully trust either, I rather give away limited data to Google rather than Facebook.

Are you freaking kidding me? Facebook, with its lax policy and 3rd party ecosystem (especially in the first years) is basically prostituting people's data.