Not sure if it's what the GA creator is determing their choice off of, but, general considerations are:

Multiple giveaways appeal less to key farmers and more to people who actually want the game, due to the higher P cost and lower odds per copy [basically, each person who wants the game gets to pay for 3 entries instead of 1, raising the total number of entries threefold for those interested in the game, while those not much interested in the game won't be as inclined to make a similarly dedicated investment].

[ As a non-grounded mathematical example:
Multiple copies: (3*1000 serious users + 3*500 not-serious users = 2 in 3 chance of going to a serious user, 1 in 1500 chance of an individual entrant winning a copy, times 3 chances)
Multi-copy giveaway: (1*1000 serious users + 1*1500 not-serious users, / 3 copies) = 3 in 5 chance of going to a not serious user, 1 in 833 chance of winning).
Again, not grounded to real odds or numbers, but as you can see off that broad-stroke exmaple, the end result of a multiple giveaway is generally more favorable to the GA creator. Meanwhile, while the overall odds are worse for any individual entrant per entry, they're likely still higher overall as well, once you factor in the rate over multiple chances. Of course, that increased odd of winning a specific game does come at the expense of lower overall "efficient" P usage- hence, again, relating to the first consideration of what audience is being targetted by a GA creator.]

Further, deletions in multi-copy giveaways, if they end up being necessary, require higher tier support intervention, to directly edit the details of the giveway. With single-copy giveaways, you can simply just put in for deletion and any staff member can handle it if you qualify for one.

Sorry, i didn't knew it was region locked :O