Electable Dictators

Bryan Caplan up at Econlog asked an excellent question:

What do the electable dictators have in common?

And he went on to offer several possible candidates like

1. The electable dictators deliver peace and prosperity.

2. The electable dictators give the people the policies they want.

3. The electable dictators are the best brain-washers.

More here.

My question is:

if electable dictators do know they will win even in a fair election, why we don't see more dictators who restrain from rigging election or usher in a regime change from dictatorship to a more open polity? What they will have to lose by doing so? Sharing their wealth and power with somebody? Wouldn't they already need to do so, at least to some degree even in a dictatorship?