Another reason QF would hand out status like candy via these promos - general or targeted (and it absolutely seems there has been a recent change to do these targetted promos but doesn't have to rull out a general one I guess, but I never expect them anyway). Anyway another reason to hand out status is in the hopes of future revenue. Sure, one could get that status cheap and then go fly oneworld airlines and use the status the next year.. but then they will drop again.. and while it has cost QF something, one still needs the 4 ~ to requalify, so there's going to be a bit of revenue there, and the chasing of status or toretain, in theory, would see a fair number of people fly again with QF to get them.
This is, of course, in addtion to the short term revenue boost from bookings made during the promo period to earn those DSC which, these days, only apply to QF metal flights anyway - so again QF figures the revenue they get from that earn, which may possibly be extra to the flying that may have been done, would offset the cost of status use later, and may just lead to future QF spend anyway.