Jared Diamond pointed out in Guns, Germs & Steel that one of the dominant factors in the colonization of the world by Northern Europe was the fact that Northern Europeans had, for hundreds of generations, spent the entire winter cooped up with their livestock. Chicken Pox, Cowpox, flu, rabies, glanders, anthrax, chlamydia, toxoplasmosis, Q fever, all have a traced zoonotic origin and Northern Europeans had developed immunity that North Americans, Asians and Africans lacked. Likewise, a lack of immunity to malaria substantially curbed Northern European expansion into Africa even after epidemics had swept through. Bugs come from critters. Critters shed bugs. Sunrise, sunset.
The amount of germs in the lab is overwhelmingly swamped by the amount of germs in nature. Not only that people don't really think of evolution in microorganisms the same way they think about it elsewhere. I mean, it took what? 50 years for pigeons to turn black? 500 years for crabs to grow faces? Fruit fly generations happen every two weeks - in a year you can get the same genetic deviation in a fruit fly that you can get from humans in 500 years. Viruses mutate like a mutherfucker and their generation time is in the "hours" range - R0 measures spread in humans, not viral lifecycle time. I can't find a number for SARS or NCOV but HIV is like 6 hours and HIV is considered an exquisitely sensitive and slow-growing virus.