All of my livebearers (so, includes my guppies) get a variety of food. I'm not specifically giving them a specific brand. I buy bulk packaging of food. Where I order them, orders them straight from the manufacturer where a lot of other brands order their food. Because the bulk packaging is not being labeled as being a specific brand, the prices are lower.
Not all brands manufacture their own food.
But also because I have a serious number of tanks running, bulk packaging is more affordable to me than buying canned food for them. And the food I order is of good quality.