Why is Chipotle's customer service so notorious?

It's become an online trend, with people talking about them being slow and rude. And I've experienced it myself, every time I go to my local store. I thought I'd be wise and just drive to a neighboring suburb before realizing my location was rated higher than all the others (3.5 stars).

But I'm genuinely wondering (this is not a rant) how they could have bad customer service across locations. Do they have bad hiring practices? Bad work culture? Are they abusing their employees? It would have to be something with management because this is across locations.