These are some reasons:
1. They want to motivate the dancers to continue what they are doing.
2. They want the women to notice them especially.
3. They are having fun and want to reward the women for pleasing performances.
4. They are attracted to the dancers and use money to make it known.
5. They know that many dancers get much or all of their money from these tossed tips.
6. It makes a man look like a big spender, and the daring ones hope to be the ones to creep with them after they have finished. That usually means more money.
7. They do not have anything better to do.
8. If men in other countries do not tip dancers, it is because their entrance fee is steep. It's like waitresses; some are paid directly, and customers pay a gratuity charge in advance, usually through their credit cards. Those dancers are working, and their skills are not free. People are basically the same everywhere, but they sometimes do some of the same things differently.
Do women in your country dance at night clubs as a free service? What woman in her right mind would work at a place with ravenous drunks salivating and eying them like hungry wolves unless they are getting big pay that they badly need? Well, I am aware that some men are gentlemen.