The anti-slavery bill being unenforced was part of the clone wars animated show that ran before Disney bought the franchise.

Tatooine also shows up in both the EU and the Disney canon during the clone wars, it’s an outer rim world that stayed independent during the separatist war, but during the imperial era became an imperialized world for its ore deposits. before the empire, it was a regular haunt of the galaxy’s criminal underworld, but during the empire, it became a hotbed of anti-Imperial sentiment. Most of its residents were either natively born on the planet, or immigrated there to work in the mining industry or to flee the law. It’s somewhat of a narrative equivalent of the fictionalized old west towns you’ll see in spaghetti westerns. People moved there either to chase the ore mining industry or to flee the law, then lawmen followed - following that the locals got annoyed at the law and fought back.