I've done some studying on cloud seeding in college. By far not an expert but took some classes on it. It requires storms to already be developing to be able to seed the clouds. All it is doing is helping the storm to produce more rain and less hail. It's not creating anything out of thin air. There is no controlling the weather just giving it a (very small) nudge. In fact, it is so minor that there's a lot of controversy as to whether it's even worth the time and effort to do but studies do indicate that it is successful in increasing rainfall throughout the life of a storm.

I think the problem is just how you define "weather". Cloud seeding can improve the probability of rain in a specific small area. But it's not viable for changing large scale weather patterns, and requires specific environmental conditions to be effective. So there's a vast difference between creating a hurricane, for example, and generating a localised rain cloud.