Again with respect you are completely missing the point.
It’s not envato who is sharing you items elsewhere, so it has nothing to do with your agreement with them not to sell elsewhere.
Nor is there anyhting at all that envato can do to stop people doing buying your item and sharing it on another site.
For example, to use your Shutterstock example:
- I buy an item then reverse it
- there is no subscription to charge a cancellation fee for
- but even if there was - how would that stop me sharing it on another site?
As @mgscoder said piracy is unfortuantely a down side to stock marketplaces - its not just envato. As fast as you close one site down they just reopen another.