This is nonsense actually, even those abuser create multiple account to receive the referral reward, they still need to have multiple device to get the reward.

If the sponsor device address is the same with the attestator device address both will not get any reward.
will people waste his time buying more device just for the sake of 10$ bucks?

I know your concern about the steem block chain, but the airdrop not make any damage as you see, actually it gives more exposure to steem blockchain.