they are, as you pointed out with the reason why they abandoned them.
And that's also why it won't change until the fines for breaking the animal welfare laws are set at higher than the cost of collecting and shipping/ killing them all properly. Paltry fines are viewed as just another (probably tax-deductible, given the idiocy of much tax bureaucracy) business expense.
I guess this abandonment would also be breaking the food hygiene and bird flu rules, because the sheds are supposed to be empty for a certain period after clearance, as part of the sanitary process, and some dead and dying leftover chickens wandering over supposedly clean and sterile surfaces are obviously contrary to that.
And they wonder why the sheds and commercial flocks are so disease ridden. Good rules have to be enforced, not just passed.