I can only echo pretty much what others have been saying here already. You can certainly win off of free spins from time to time but the likelihood of actually winning something of any sizable amount or winning every often is just not that likely.
Ive won on free spins before in the past but its been quite some time and I never had won anything of much.
Free spins are still good though since they can be a source of small profits somehow, but if you wish for significant amount of profits, you will not likely to experience it from free spins. You have to deposit a good amount of fiat so you can bet big and win big. That is most likely possible with high rollers since they have high bankroll ready to finance their gambling bets. However, I have not made significant gains from free spins, only small winnings that I almost forgot how much it is.
Winning some money with free spins is indeed possible but just as you mention winning a lot of money is not possible as casinos are going to limit the amount of free spins they give to each one of their clients.
Free spins are just a bonus that is given by casinos to give their players the opportunity to experience some of their games for free so they can identify if they like those games without the need to spend their capital, which is valuable in itself as there are some casino games that you could have never tried on your own if it was not for bonuses like that.