There will never be any forms of advertising where we get 80% of people to like or share content. Never. Even organic posts by users themselves don't see this type of engagement. Most are lucky if they get 1-2 likes per post. The fact that brands CAN get these engagements says something.
Also, though the numbers may seem low, the cost of these posts is low and when combined with other forms of advertising along the purchase funnel the ROI is worth it.