Why Do Companies Give Away Free Stuff?
Understanding the economics is the fastest way to judge a giveaway, because a promotion that makes no commercial sense for its company is usually not what it appears to be.
They are buying a mailing list
A single gift card can produce thousands of email addresses with stated interest in a product category. Measured against what a company otherwise pays to reach those people, the prize is inexpensive. This is the main reason and it is not sinister.
And attention at a moment they choose
Promotions cluster around product launches, seasonal peaks and store openings, because a giveaway concentrates interest on a date the company running it picked. It is why volume spikes between Black Friday and late December.
What this tells you
A giveaway attached to a real company, a real product and a real marketing motive is very likely to pay out, because the company running it wants the list and the goodwill more than it wants the prize back. A giveaway with no identifiable company and no product has no such motive, and you should ask what it is actually collecting.