So, using your logic, why doesn't this same long-term 'no-divs' issue constantly crop up at all the other large UK airports too? Do they pay the wages for their handling agents? Do they subsidise them? And it's not confined to divs either. Requests for series of cargo flights notified well in advance hit the same predictable wall of 'no-can-do' at MAN.
Your solution amounts to shrug the shoulders, blame someone else, and continue to let the low standards drift on unaddressed indefinitely.
Identifying the problem does not absolve management from striving for a solution.