1. Antibiotic misuse is rife. Most of this is in third world countries where its use is unregulated. Crops and herds are administered multiple antibiotics to ensure a healthy return.
2. Antibiotics are misused by the public. In Spain, you just buy them over the counter. In the UK, most GPs battle against the misconception that all colds and flu can be remedied by antibiotics. Everyone seems to think they have a "chest infection". Some GPs are crap and just give in.
3. Bacteria multiply. Fast. That means if one bacterium has resistance, a resistant colony will spring up overnight. They have effective means of transmission through pus, sputum, aerosol particles eg coughing.
4. Bacteria love to share. This is the dangerous bit of all. If one colony had resistance, it would still take a long time for all strains of a particular bacteria to become resistant. They are share strands of nuclear material. Imagine you could exchange knowledge with say a professor just by holding their hand, and suddenly you have the same level of knowledge as them! Suddenly bacteria that are responsible for one type of infection don't just develop resistance to one antibiotic but could potentially develop resistance to them all, despite never being exposed to them.
5. Developing antibiotics isn't very profitable for drug companies. They don't make much money out of them these days so there's no real drive to create new antibiotics. Anticancer drugs sre the latet craze. I suspect once things become dire, they may change to researching new antibiotics.
6. Bacteria have been here for years. Far longer than the brief millisecond humans have been here. They survive in extremes of climates. They can withstand nuclear holocaust. They will be here long after humans have disappeared from the face of the planet. A few puny tablets aren't really going to stop them now, are they?

I am not so worried as I have a very strong immune system. I avoid antibiotics if I can and rarely take them anyway. Good news is that it will cull the elites and plebs alike.

It's been general knowledge that we've been over using them for years.

Farmers are among the worst abusers. Though it would ease the over crowding problem in the London if a large slice are killed in some pandemic, it might help the unemployment problem as well.

And make house pries more affordable