alt Hacker NewsDiablo 1 had no running or speed mechanic, movement speed was always constant. Its expansion Hellfire allowed running in town but not in combat areas.
Diablo 2 (2000) added the sprinting mechanic with limited stamina, but it panned out as irrelevant for gameplay. The stamina supply easily ramps up to more than you ever deplete so you just always run. And players wanted it that way since no one wants to walk slower, and the monster speeds were later increased to be balanced against players always running.
Not all gameplay mechanics need to last for an entire game. Stamina as an obstacle that you overcome plays into the power fantasy aspect of the game very well. Arguably it goes a long way to offset the feeling you’re slowly falling behind the power curve which is how they get people to grind without complaining about poor balance.