It's because SE does not organize these, they provide the prizes and codes, but these companies are doing these promotions and they're used to the customer base being pretty lax about their promotions.
No one is going to be too pressed about a mountain dew t shirt from a promo messing up. FFXIV players are way more invested and have expectations others don't and the companies aren't prepared for. Also with most of those a big holdup is that the company vastly underestimates their sales and doesn't order enough codes from SE until they have mad players blowing up their customer service department.