Because the people in power are terrified that just maybe there actually is some funny business going on and they are benefiting from it (by having been elected

Because the people in power are terrified that just maybe there actually is some funny business going on and they are benefiting from it (by having been elected), and if they fix the system they will lose the next time around. It’s probably an irrational fear in many ways, but there’s always that little bit of them wondering. Also, they could have granted long term contracts to existing suppliers, don’t have a budget to replace existing machines, don’t want to make the person who bought them look bad, or even possibly don’t want to say the old machines are bad because it calls into question the integrity of past elections.