In retail, it's often referred to as.... LOST LEADERS
for the cost of lost profits and small internet profile, which gets shared n shared n SHARED (most competitions get advertised in several, freebie sites n FB pages, blogs etc). People then enter, of the volume of entries, a percentage go on to anker.com to see who is doing the competition, of that number another percentage would buy. These purchases far outweigh any costs n lost profits.
It's the same in a supermarket when the end of isles have deals... BOGOF, 3 for 2, it 2 for ?? .. did you know that the supermarkets make the companies pay for this premium space themselves.
It why milk, is often at the furthest back of the store, so those who pop in for a pint, have to walk through the store.