The free spins won't allow you to win anything. It is just a promotional tool to draw you in so you play more. Its just like how casinos will givep layers free rooms and free food so they stay longer and play. For whales they give them the most ridiculous perks and even let them fly the casino's private jet just so they bet millions.
So these are just a strategy to make more player for them? We are never going to win those free spins 
You are correct winning on free spin is very rare. Plus you still have to do roll overs before you can withdraw if ever you win from free spin. Its just a marketing strategy to get new users.