Part of the reason why so few in their society, pre-rise of the Dark Lord and post, ever even considered trying to procure their own batch of polyjuice potion was simply because it was an incredibly difficult potion to brew correctly. If she was completely honest with herself, it was an absolute miracle that Hermione was able to brew it successfully in her second year. Her issues with the cat hair aside, if she had made a single mistake in the brewing, all three of them could've been killed or irrevocably mutilated. It wasn't safe to have the average brewer even attempt it. The laws in place making it illegal were also there for everyone's safety. Wasn't it better to just ban the dangerous substance outright than to allow another incompetent potioneer to hurt themselves? Besides, polyjuice potion took too long to brew. Few had the patience to wait.