Players are the ones who prefer to say DPS instead of Damage Dealer or DD. Game developers have adopted what players are familiar with.

Good luck with your crusade to convince hundreds of millions of players world wide to use DD.

Also "DPS" would technically be a noun as it is referring to a calculated value. Colloquially it has been adopted both as a noun (a role performed) and a verb (the action the role performs to generate the numbers used to calculate the value). Welcome to the evolution of language.