If you find out, please tell me!
Actually, you need to do two things
1. Ask him to help you with defined tasks- don't say "I never get any help around here"- say "would you help me to take out the trash/make the bed/ wash the dishes" and you need to ask when you need help and not expect him to remember that it's "his job"
2. Lower your expectations. Be glad when he helps, but don't expect that he will always help on an equal basis. Thank him sincerely when he's been helpful and tell him how much it means to you.
Some people are naturally helpful and ambitious. Others can learn if they are motivated. If you make your peace with the fact that you are not going to get everything you want in terms of help, you will be a happier person. If you grouse and fight about it, I can guarantee, your chances of getting him to help are going to decrease.
Good luck!