It's what bad guys do you know? They're duty bound by all the conventions of literature, cartoon, drama, whatever to behave in a certain way.
Bad guys never kill the hero, or heroine, when they have the chance. It would be really easy for the bad guy to pull a gun and shoot the good guy. But it never happens. It doesn't happen in the James Bond films, it doesn't happen in the Indiana Jones Films and it doesn't happen in cartoons that, in some small way, take the mickey out of the above, like The Perils of Penelope Pitstop, Hong Kong Phooey and so on.
Bad guys always dream up convoluted plans to do away with the hero, or heroine, involving long slow tortuous processes with trains, rope and blades. Why this should be is anyone's guess, as the bad guy does not intend to be around when the execution is actually carried out. Bad guys, I guess, like planning. That would explain it.
Bad guys always explain their plans, in great detail, to the hero, or heroine, before setting the complicated apparatus in motion. (An episode of the fabulous Animaniacs actually had the Warner Brothers (and the Warner sister, Dot) stop the bad guy, take out his contract and point to the paragraph which stated that he was contractually obliged to explain his plan in all relevant detail to give them time to think of a way to escape.)
Bad guys have thick henchmen. They're usually square too - very strong, but with no intelligence at all. They alway bumble and scupper plans. They never help in any way whatsoever.
Bad guys, when their plan has failed, will then take a gun out and start to shoot. They are lousy shots. Very, very poor at it indeed. It usually takes the good guy only one or two shots to do all the necessary damage. On a good day, a bad guy can shoot as many rounds as he likes and still only graze the good guy's upper arm.
Due to Arnold Schwarzenegger, bad guys, now, always say 'I'll be back' or words to that effect. If they don't say it, then they are aware that they are not saying it. Arnie wrote the rules on this. These words are either said or consciously not said. There's no half way house on this one. On cartoons, bad guys are duty bound to say 'and it would have worked too had it not been for you pesky/meddling kids'. Scooby Doo is responsible for this one. The same principle applies.
British films usually have Scottish bad guys (Sean Connery crops up a lot, I feel), and American films always, always have English bad guys (so much for Anglo-US relations, I suppose): they are always impeccably groomed, quirky in the extreme and, more often than not, played by Alan Rickman.
Bad guys are always defeated (it they're not, then, technically they're not bad guys. They're villains, and there's a difference).