It’s more about how you want/need to promote your product.
If it’s something that people are actively searching for, or solves a problem that people may be researching for a solution to on Google, then you should be advertising on Google.
If people wouldn’t ever be searching for your product then a solution like Facebook may work better. As a display ad network, you can get your product in front of lots of people who would have otherwise never been exposed to it.
It is often the case that both platforms are used together, as they have different strengths. Obviously there will be products that don’t get advertised on each platform, but that is often just down to a gut feeling – if you are selling a b2b product for example, lots of marketers would turn away from Facebook, that doesn’t necessarily mean that a b2b product can’t be sold there, with the right targeting and message it could do really well.