The reason not to postpone development is because it isn't a particularly quick solution. It would be one thing to develop and test them, and then postpone deployment of them. It's another thing to not have a backup plan and hope that one of the antibiotic candidates work out, and quickly.

Modern cities are a huge disease vector. That kind of population density lets sickness run rampant. Untreated TB has something like a 25% mortality rate, and we've already seen drug-resistant (DR) and extreme drug-resistant (XDR) strains of TB. An outbreak of TB that we have no antibiotics for would be devastating.