Its within six feet for 15 or more minutes
Or if you are coughed/sneezed on.
I'd agree that within 6 feet of an infected person, maskless, for 15+ minutes makes it pretty likely that you'd catch the virus. But it's not like the virus cant travel more than 6' or someone get infected in under 1 minute. It's pretty arbitrary/general guidelines.
If everyone wears mask it's very good double protection. If Trump circa March 1 said that everyone needs to wear a mask in public to combat the virus. That it will take some getting used to, and he's not thrilled about it, but masks are the main way to limit transmission and defeat the virus. Everyone would have been on board, and if even 10+% refused out of some misguided stupidity, the US would have been safe and the virus would have been contained in 2+ months. That's all it would have taken, for Trump to set an example, wear a mask and tell others to do the same. And have his medical team do the same. And then to organize testing properly and contact tracing.
Over 100K Americans would still be alive. A million or more wouldn't have gotten sick. The economy and normal life would be back. Maybe folks would need to wear masks, and be able to have a normal life/country again. 60 cent masks ..