My question is why do members move from one campaign to another?
It's the same as asking why people change jobs, or why they go to different restaurants or shops - everyone has their own preferences that make them choose what to promote at a certain moment.
But I have seen where members go from better pay rates to the ones with lower rates and lower posts requirements.
For some, it's not all about pay rates, but also about what they promote, and if the differences in pay rates are very small, then it makes sense to choose a campaign that is less demanding, regardless of whether that campaign pays less.
Three years is like a lifetime, both for the campaign running and the member who remained faithful to it.
I was also in one campaign for more than three years and I don't see anything strange about it - you have excellent conditions, an excellent campaign manager and you are promoting something that you think has benefits for the community.