You didn't reflect, why different microstocks lower fees, the salary to the authors?
The answer: the Example, at you in portfolio of 3000 photos.
You have loaded them on different microstocks. The buyer will go hardly on another microstock, because there the same works as well as here, identical.
Means at microstock not especially strongly buyers and microstock increase then reduces fees to the authors to pour in money in advertizing and so to struggle with competition.
It turns out, ourselves create competition and we promote fall of our deductions...
Ourselves dig to ourselves hole, or we saw bough on which we sit.
Exclusive works and authors - allocate microstock from its competitors, do it not similar to others and by that involves more buyers.
Therefore, if we want to sell successfully further the works, it is better to become exclusive authors.