As the accused you can appeal. So if you found guilty and then there is new evidence, better science, an impartial jury etc you can appeal and argue you are innocent. But if you are found innocent the state can't do the same.
Let's say there's a murder 5 years before dna evidence is discovered. The state accuses someone and puts them on trial and a verdict is declared. Now dna evidence is discovered. If the person was found guilty they can file an appeal saying based on this new dna evidence they can prove they are are innocent. If the person was found innocent however the state can not file an appeal saying based on this new DNA evidence now we can prove that person did it.
State gets one shot at proving you guilty, you get multiple to prove you're innocent.