People are vocalizing their lack of trust in the government to serve justice in part because cases where people whom they feel deserved more punishment didn't receive it and similarly with people whom they feel didn't deserve as much punishment as they got.
An example that comes to mind is that for all the layoffs happening lately in the tech industry, a common sentiment here on HN seems to be that CEOs are talking about taking responsibility but usually don't really face proportional negative consequences to demonstrate how they're doing that. Similarly with criminals, of course you can and should rehabilitate them to prevent re-offending, but if that's all you focus on, you kind of miss out on making them take responsibility for their actions.