I believe it was Stalin who said something like (can't remember the exact quote - I paraphrase), "if you murder one person it's a crime, if you murder thousands (?), millions (?) it's just a statistic".
And I believe that there are many people in positions of power, throughout the world, who know that this is still true. They also know that the world will let them get away with it, for a while (will even supply them with the weapons), and if their crimes become too revolting the worst that they can expect is a fair trial (with the possibility of being acquitted) and a comfy cell with full amenities.

Normally, I don't support the death penalty (except for crimes involving great cruelty) but genocide and organised mass murder are NOT the same, either qualitatively or quantitatively, as murder within 'every day' civil society (extraordinary and terrible as such a crime may be).

The penalty for genocide and mass murder HAS to be different from 'ordinary' murder because it is different and we are all in extreme danger from it happening to us.