Basically an IQ-meritocracy requires a market based system, exchanged based one, where what you get is very roughly proportional to what you give to others. However most of the planet is not exchange based but power based. This is where intelligence is less useful.

Intelligence is very useful in conflicts. If you can calculate beforehand whether you will win or lose a battle you don't have to fight the battle if you think you will lose it.

In our modern world great intelligence means the ability to hack computers. Getting information and being able to alter email message that person A sends person B. That's power.

Getting money because you are smart enough to predict stock market movements is another way to get power.

And of course it can very well be that you don't want power, you want to be a researcher... but in that situation you are forced to take orders from him so you may still want to topple the big boss or something.

Stalin was likely powerful but a lot of today's political leaders are less powerful.

Peter Thiel made the point that Obama probably didn't even knew that the US was wiretapping Angela Merkel. It's something that the nerds in the NSA decided in their Star Trek bridge lookalike.