If a person has been convicted of an offence they haven't committed. Spent years in prison, lost their self respect, their jobs most of the time their family. They have been treated like dirt in prison and there are recrimminations because they are maintaining their innocence.
They manage to get a retrial and been found innocent of all charges. Then they find they can't claim compensation for what they have gone through. They can't get a job because even though they are found innocent, mud sticks. They have to go through the process of explaining why they were in prison.
On the other hand, it is easier to get compensation for the complainant once they have a conviction. On top of that they are not made to pay the money back if the defendant has been released after being found not guilty.