The trick is that you can't know that an infected person wasn't in there before you. Maybe it's not your coffee shop, but with 10,000+ infected people in the country, if every coffee shop had 5 people in it, someone in one of them would be infected. The virus has been shown to survive on surfaces for some time, minutes to days depending on the surface. So, one person in one coffee shop infects 3 or 4 people, they infect their families, they go to a coffee shop again 3 days later and now they contaminate a surface, and now you've got a cluster of 20 people infected and you probably kill someone.