Dictators, by definition, reduce choice. This implies slower economic growth. For example, they may siphon wealth into their own pockets, put incompetent friends in key positions, divert money into building a police state, etc.

This is impossible with ground rent. Changing to ground rent would create many bilions of dollars of new wealth.

So a dictator can secretly be offered an enormous bribe to allow ground rent. He can remain as a purely symbolic figurehead in a palace, and will be richer, more loved, and safer, as a result. With not one drop of blood shed.

(If he refuses, the same billion dollar offer can be made to his generals. If he wants to live he will take the first option.)