Higher Reward is the only key 
Especially if you are a high-rank Member and I do believe this is only the reason why members keep switching from one campaign to another or there is another reason is helping the project or friend but this is small chance of happening to Bitcointalk
I wish I could do that But Low Rank and low merit like me is no way to keep switching between campaigns. If you are a high member and have high merit at least get recognized by the other high member have trust list in DT1 or DT2 you can easily move one to another for a high reward of course I could see 1 person can easily get 6$ post or more in one campaign
Especially if you are a high-rank Member and I do believe this is only the reason why members keep switching from one campaign to another or there is another reason is helping the project or friend but this is small chance of happening to BitcointalkI wish I could do that But Low Rank and low merit like me is no way to keep switching between campaigns. If you are a high member and have high merit at least get recognized by the other high member have trust list in DT1 or DT2 you can easily move one to another for a high reward of course I could see 1 person can easily get 6$ post or more in one campaign