How has Rwandan minority been able to control govt. for 20 years?

I'm watching Hotel Rwanda. So I looked up Wikipedia on Rwanda. The TL;DR seems to be: 1) Hutus are 84% of population, Tutsis are 15% 2) Tutsis are the historical elite and ruled the nation (not unusual) 3) Democracy was ushered in at some point and Hutus started ruling 4) Tutsis didn't like it so they formed a militia 5) Cue the genocide when Hutus killed a million Tutsis (1994) 6) Since then, all democratically elected governments have been controlled by Tutsis (a tiny minority). The current president is a Tutsi. How the heck did (6) happen? Anyone know?