Actually there are plenty.
The infrastructure doesn't exist and at the moment cannot. Fraud would abound. At least with elected officials you know for certain who voted for what and what the process was.
Additionally, there are limits and processes involved in submitting and ratifying bills. Give millions direct access to propose and vote on items and that system becomes unmanageable.
Then there's the fact that the idea of IQ being of benefit assumes that such "high IQ" voters both have the inclination, time and other resources to examine all bills and related information, they won't, they'll have other jobs. IQ is nice but one still has to apply that to knowledge.
Then of course we come back to the basic point underlying all this and that is that governing and building a society isn't a matter of pure mathematics as though a calculator could sort it out. In politics and society the goal line isn't fixed, in fact, one could argue it's not even defined. What's the end game of society? Does everyone agree on what's most important and where we should be heading and how? Individuals of any given IQ can differ massively on a way forward because of the differing values they place on things. What's more important, material prosperity, technological advancement, the pursuit of pleasure, freedom of expression? There is no 'right' answer that can be calculated and so IQ is only a part of the equation; the answer is subjective, we define for ourselves what the goal and purpose is. If that's the case, if human choice and desire are the bottom line, then the individual is of maximum importance and there is no way to say that an irrational or silly choice or plan or desire is any better or worse than any other. All we can say is that there are different plans and we'll all pitch in our voice and go with the majority. That, theoretically, is democracy. No 'right' or 'wrong' just the majority. Thus, everyone's voice counts. Who can say any differently?