Nidoqueen are said to be the Queen of the Safari Zone, a majestic pokemon fit only for royalty. History has shown them to be far more popular among usurpers, petty lords and dictators than actual rightful kings. Giovanni's Nidoqueen is the latest in this long tradition.
There are some who speculate that the fact that they have Nidoqueen is why these tyrants are able to gain power, and not the other way around. It is true that they are powerful pokemon, with tough skin and the ability to create earthquakes when they stomp the ground: many have strengthened an army, but they are not so strong as for a single one of them to be the difference between victory and defeat in warfare.
The reality of the situation is equal parts tradition and megalomania. Those with pretensions to monarchy catch Nidorina and search high and low for moon stones, in the hope of legitimizing themselves through their possession of a pokemon of monarchs. But it is also true that Nidoqueen are pokemon which love luxury and battle and spur their trainers to seek the power of a king, so that as a king's pokemon they can win for themselves a power not unlike a queen's.