If you exclude your contacts and friend lists and exclude friend of friends, who does that leave? Friends of friends of friends? Complete strangers? I wonder what proportion of couples knew each other directly or indirectly before they got together: "Oh, you know Jack! Yeah, he's by father’s brother’s nephew’s cousin’s former roommate!"
Obviously I have no hard data, but it's not too difficult to imagine that couples come together with all sorts of varying prior knowledge of each other's existence.
That the current meta is this, doesn't mean that is the most successful strategy for all people at all times.
I think dating apps suffer from the public health policy vs. individualised medicine paradox: what might be good policy for people en masse might be terrible advice for any particular individual.