Because they've been here a lot longer. They have a resilience. You're not gonna destroy them. We're not gonna get rid of them. I haven't heard recently of a bacteria facing extinction.
Antibiotics are a powerful weapon.
But every now and then, a mutant bacterium will have some genetic quirk that allows it to withstand an antibiotic. With no competition for nutrients, it grows and multiplies. It is the paradox of antibiotics that the more you use, the more resistance you breed. Since antibiotics arrived in the 1940s, doctors have prescribed them with glee. U.S. research suggests that only one in 10 people who are prescribed antibiotics actually need them.