I notice the same thing in my area - shops still hand out bags, and there's plenty of them lying around near trash cans. The thing is, bans usually get introduced in stages and aren't uniform everywhere. In some places it's a complete ban on single-use polyethylene bags thinner than some specific micron thickness, while in others only thick bags are prohibited. Nowadays a lot of shops have switched to thin bags made from biodegradable material or paper - they're still called bags, but technically they're different. Plus not all shops follow the rules equally well, especially the smaller ones.
Second thing - fines are often purely symbolic or simply rarely handed out. To fine a shop, you need to draw up an official report and prove the violation, and that takes inspectors' time. For big chains it's usually easier to just pay a small fine than to completely overhaul their equipment and retrain staff on handing out different types of bags. So the ban exists, but it works in a pretty half-hearted way.