The moment you realize that, even though this is a fictional story, there have been countless cases in Real Life of innocent African-Americans (or people of color) sentenced to life imprisonment simply due to systemic racism and/or for exploitation of labor. Despite being a comedy, the premise still doubles as both Nightmare Fuel and a Tear Jerker.
...Plus, the horrible fact that it still occurs even today.
The fact that despite finally escaping and gaining their freedom again, it is 1997 and they are both 90 years old. While they are in good health for their age, it's highly unlikely they would have enjoyed their freedom for too long. Assuming - for instance - that both live to be around 97 years old (which is quite possible), that would only be seven years of freedom before death (and that's assuming they do live for that long afterwards). And because of their age and limitations, they can't really do all that much with themselves anymore; they can't marry, have a family or really explore the world much; being escapees from prison also means they'd probably have to be careful who sees them. They may be content with simply living their final days in peace and away from prison, but this does hammer home the title and message of the film; their whole lives were taken from them and not even actually getting their freedom back changed that.
