Yes, it makes them happy, actually the feeling of happiness arises because of a misunderstanding regarding their perspective on the bonus, I am sure that they feel happy because they think that the bonus will give them a number of wins, when in fact it is still a "possibility", in the sense that the bonus comes not to give you a win, in this case the casino is very smart, the dealer knows about what can trigger joy, hope and confidence so they provide bonuses as a facility, actually it is not to give free wins to gamblers, but nothing more than just to increase the gamblers' hopes for victory because the casino knows that when a gambler's hopes and beliefs increase, the possibility of various more aggressive actions will increase.
You can even imagine a situation where a player has lost his deposit and was given free spins after that. And on free spins he is lucky and he wins, after that his confidence that he was just unlucky with his real money at the beginning, but in fact in the game you can win constantly and use it as earnings simply to strengthen. And even after several deposit losses he will not stop, he will simply think that he is a little unlucky. In short, free spins can only strengthen the player's faith, and casinos have come up with them specifically for this and of course not at a loss to themselves.
Yes, the point is that the free spin bonus given by the casino aims to trick and play with the feelings of gamblers, there is no free lunch, and they should realize that there are no significant results with just a little effort. So gamblers should not feel disappointed or upset when it turns out that the results of the free spins look bad, because after all free spins are not a sign that you have cracked the code to win, in the end it is still luck that determines whether you will win or lose.
In the end, this is the reason why understanding the concept of gambling is very important for a gambler to have, because then whatever scenario you experience when gambling should not change your perspective, hopes and beliefs about winning.