[2020] Why do we have stamina in 2020?

It's a survival RPG. It'd be surprising if it didn't have stamina. You could make the same argument that limited carrying capacity, or even other core stats like food & water, are also "we want you to play but actually don't" mechanics.

If you're just standing around, there's no polite way to say this... you're doing it wrong. I feel like stamina is fully integrated into many areas of the game at this point, and there are a huge number of ways to mitigate it in different scenarios:

• Use drinks that temporarily raise your stamina recovery.
  
• Use good food to temporarily raise your max stamina.
  
• Use skills that permanently lower stamina usage in particular activities.
  
• Use skills that provide a stamina bonus, typically on zombie kill.
  
• Use a lighter/more primitive tool until you can handle a heavier, more stamina-intensive one.
  
• Use mods on your tools to make them more efficient.
  
• Wear less or lighter armor.
  
• Use power tools or vehicles so you're not working under your own power in the first place.
  
• Change up your rhythm. For instance when mining, mine the ore until your stamina is low, and then switch to a 'resting phase' mining the softer gravel while your stamina recharges. When cracking open a safe in a POI, use the downtime while waiting for stamina to recover to loot the easier containers in the room, reload weapons, free up room in your inventory, repair items, or go about other maintenance tasks. When running long distance, pause for a second to loot a trash pile or a bird nest, giving your stamina a second to catch up.
  
• Reduce the need for stamina-intensive activity. For instance, if you increase your mining harvest or scrap harvest amount via skills or candy, you'll get the same amount of resources in less time, and thus for less stamina expenditure.
  
• Find alternatives that don't require stamina. If you're losing your stamina from mining coal and nitrate to make gunpowder for example, maybe instead you'd prefer to spend your time doing quests, that give you Dukes, that you can use to just buy gunpowder from the trader.

Those are eleven ways I can think of. So the game totally provides multiple solutions to the stamina problem, and in my humble opinion it's a fun problem to overcome. The design is sound.