Because there is no such thing as karma. Do you really think that someone will get magically punished by some invincible force? Fairy tales don't exist in real life.
It's only when you or other people act on someones bad behaviour that there are any consequences. But people not always care and governments have other priorities than fighting small "crimes" so often bad actions go unpunished.
So the kick in the ass has time to wind up and hit all-the-harder. 😈
Have you considered that there is no Karma at all? Powerful people are capable of getting away with all kinds of nasty things. The notion of Karma has been invented to bolster the social order and keep the masses peaceful. There is, of course, some truth in the notion of Karma because there is some tendency to reap what you sow in the world of humans. But a lot depends on your place in the pecking order.