Do you see a reason why the "per 100,000 population" wouldn't correct for population.

Maybe their justice system doesn't work very well.

Or maybe it works very well.

There are different reasons why a country might be low on the list. Maybe they have little crime, maybe they fight crime without locking people up for long periods of time, or maybe they lack the resources to fight crime.

If a country is high on the list, it could be they have insanely high crime, but it could also mean that they punish much harsher than other countries, or crime is not the primary motivation to lock people up.