Because you store vegetables in fridges, and you can make a pun, I guess.
This is what the Vegeta fridge ads typically look like, and they have been around for a while without an overt Dragon Ball nods. They have been "Vegeta" as in "vegetables" and not as in Super Saiyan.
But now, no doubt, Toshiba could not resist bringing in you know who.
This isn't the first time Vegeta has been roped in to sell a vegetable type product. Last year, he was selling vegetable ramen.
I wonder what vegetable items Vegeta can sell next year? Hopefully some health drinks.