If its illegal to put up flyers around Dublin city - then how come people do it??

My understanding is that it is illegal to put posters / flyers on telephone poles etc around dublin city. Seemingly - its considered littering and you get into trouble with the council. How come then people do it. Fitness bootcamp is one offender and spanish dancing is another. There's phone numbers and business qddress are clearly printed on the posters. How can they get away with continuing to put up posters??