Kak Klaxon,
Sounds like an attempt to pay even less for ground handling than please their customers.
Think you've got it in one, mate.
There is no way a bag of 10kg size will fit in a dash locker, so the cabin crew will have to take on this extra unpaid task of 'loading' the fwd baggage hold with all these oversize bags, lengthening the turnaround, possibly delaying the flight.
T=