$0.02: I can't prove it, but I think it comes down to the line itself being a mode of advertisement. You wouldn't want to eat somewhere unpopular, and a hyper efficient drive-through would give that appearance. To blunt the impact of a deliberately slower drive-through, they put people out front* to greet customers so they don't feel ignored in line. This in itself is something other chains don't do and, instead, have to crush the drive-through line fast, just to keep everyone's blood pressure in check. It's better "customer service", but as OP illustrates, places your staff out in the elements.

Meanwhile the food is bland and factory-assembly-line consistent, with toppings that range from bland to sweet and bland. Perfect for kids and adults that already have enough excitement in their lives. Are powdermilk biscuits on the menu yet?

(* if this is a corporate-mandated thing, it's freaking brilliant. A manager can't realistically pull one of the greeters to handle a kitchen disaster in the moment, since they're outside. So, service in this regard is hard for management to screw up.)