In addition to the answers that say it's riskier to get the vaccine than to be vaccinated, rabies is also the oddball disease where you can be vaccinated after exposure - it moves through the nervous system so slowly that it can take years to get to your brain. Of course, if it does, there is roughly a 100% fatality rate, but if you have an expected exposure (get bitten by a wild animal, or suspect you have been) there is still plenty off time to get the vaccine and have it be effective. This is a more cost- and risk-averse approach.