Casinos know how to play with psychology to keep people coming back. They design everything to make you feel like you're always on the verge of winning, from the bright lights to the sounds of coins clinking.
This is why they don't stop marketing, they do their marketing like they are trying to help gambliers, even he day you don't have money and you seems to their regular customer, they will offer you free bonus to gamble but they are doing it because they don't want you to take away your attention from their casino, using the bonus is a strong message for attention because they know you wouldn't win.
For the casino, I will say it makes sense but as an individual, it's 50/50. If you are very good in gambling, bonus are easy to make more money you know but a novice will waste it without winning anything.