We aren’t finding new antibiotics anymore because there are only so many human-safe systemic vulnerabilities to take apart/stop bacteria metabolism biochemically without moving into the genetic arena for further variation. What we are really exhausting are the biochemical differences between our cells and the bacteria cells by wiping out things that make the bacteria unique. This is really bad because it drives additional compatability with the human body while eliminating ways for our immune system to tell them apart as well. We have been driving the evolution of bacteria toward this since we discovered penicillin. What we need is to introduce new genes blocks into wild bacteria that make them susceptible to artificial compounds we create while also conferring a survival and even reproduction advantage to them over bacteria that lack the implanted gene blocks. This would balance out the evolutionary force of the artificial compound vulnerability. I’m fully expecting the Jurassic Park chaos mettling with nature speech but we have precious few options when completely resistant strains of new lethal bacteria inevitably emerge.

But isn't that just a market problem? Once resistance is widespread, won't companies be incentivized to find new antibiotics?

There are presumably a finite number of chemicals that are of the right molecular size to get where they need to go, kill a reasonbly broad range of bacteria, and don't harm humans. We may have found them all already.