Precisely and we are seeing this. The problem is that their tech does not align with their promise to the customer or the customer expectation:
When a customer deletes a file his expectation is that it gets deleted immediately and that he will not get billed for it any longer.
However this is not how the Storj tech is working. I am not sure now with haststore but with piecestore there were those bloomfilters periodically created from backup data, then some time later if the deleted data is included in the bloomfilter the pieces were moved to trash and after that finally deleted. AFAIK all of that unpaid for the SNO. And as you have said for Storj no incentive to create find a different process that uses less disk space, because for them it is free space they can use however they want.
For SNOs of course it is not free space. It is space that is occupied by Storj and cannot used for anything else. But they bear the cost.
There was more or less big discussion about that in the past: