More than 70% of antibiotics manufactured are fed to animals on factory farms. In order so they live through so disguisting conditions that other way they would die. Because of the scale of the industry there is a high chance of a bug mutating that is resistant to antibiotics.
In 2017 UK government released a report that the threat to humanity from antibiotic resistant super-bugs is greater than from climate change.
A post-antibiotic era means, in effect, an end to a modern medicine as we now it. Things as common as strep throat or a child's scratch knee could once again kill –Margaret Chan, former Dir. General of WHO