Not only are there **lots** of other plausible causes (of just one I gave you), you havent even explained the direction of causation.
A very simple explanation (again among many possible ones) is that being poor causes low intelligence rather than low intelligence causing one to be poor. If you are poor you wont get proper nutrition or education, both of which results in lower intelligence.
That said youre extremely low-intelligence answers are doing a remarkably good job at convincing me we should exterminate you at least, so you are least making a convincing argument, even if it isnt the argument you intended to make.