Food is universal, and it has been proven that humans are born with a desire for sweets. Promotional sweets have several advantages over other forms of promotional materials. Pens are often ubiquitous offerings, and they can be a poor choice if given away at a business convention where dozens of other companies are also giving them away.
A potential customer who walks past with a bagful of pens will turn down one more. Promotional sweets and chocolates, on the other hand are always appreciated and rarely turned down. People are also more likely to return to you for another sweet after they’ve finished their first!