He only has, like you say the possibility of ruling for life. Maybe he does a great job for 30 years and then they get rid of him. He still has to be voted in. Also if you got to El Salvador you will understand just how insanely popular Nayib is.
Discussion
Maduro was popular too, look how that turned out. Who would have thought that a government that can arbitrarily incarcerate people would be popular?