Most of the time, the bonus comes with a tough wagering requirement. It is not like that the casinos do not want us to take free money, infact they do not want the bonus to be abused.
If I tell you about my personal experience, I could not fulfill the wagering requirements of any bonus or promotions in which I participated, but I am sure there may be gamblers who have won and could cash out the bonus money. Is there anyone who can share their experience?
Tough or not tough, it depends on your budget for gambling to meet wagering requirement in a bonus program or a contest. It's up to you in consideration before joining and after you agree to its terms, there is nothing to complain about wagering requirement later.
I agree that many programs and contests have wagering requirements that are impossible to achieve by small gamblers, so they have to consider it more carefully before joining. Before joining for nothing, and be not eligible at the end is very unwisely and kind of wasting your time and money. Wagering more means more risk to lose money if you are not experienced with gambling and wagering.