The old tired counterargument: nobody colonized Earth's cloud-tops yet, and they sure are easier to get to.
Also, if you have the means to colonize Venus, you don't need to colonize Venus anymore. The ship that took you to Venus is a better place to live in that the colony.
And the obvious counter-counterarguments:
I was wondering what people thought of this paper by Geoffrey Landis on colonising Venus. In it he suggests that cloud-top Venus is one of the most benign environments in the Solar System. Temperature and gravity are similar to Earth, there's some radiation shielding and useful resources, and aerostats filled only with breathable air would float at that height. I'm no expert so can't speak to how accurate it is, but it's certainly very thought-provoking for such a short paper.