Well, we are 102. And not because of benevolence (even when we have a lot of soft judges lately, that seem to prefer to look after criminals instead of the population), but because our prisons are old and full of people, and there's no political intent to build more. (The government even destroyed some cuz they were too old, but didn't replaced them)
I bet that a lot of poor countries down there share the same reasons (and maybe, some lack the money to build more).
This is ~0.5% at a given moment. 2% over 10 years doesn't sound too much.