The problem is the commercial model for funding and research, as a new antibiotic is guaranteed to be a commercial failure, and the risks are high.
If EU, US and maybe the Chinese funded research - both universities but also in some way that it would be economically interesting for commercial entities, there would be new drugs.
This is not axiomatically true.
A change to the model where the government(s) develop their own antibiotics so that they can sit on them might be in order. It's not much of a vote winner but is as essential as defence.
Another way is to shelve the start of the patent window along with the drug. If we know it works but it's not needed yet, don't start the countdown to patent expiration until it is needed.
The former perhaps lowers costs for the drug more effectively. The latter gives more incentive to the drug companies to keep doing their research.
You have to remember the time constraint on drug profitability (~15 years for a US patent on a new molecular entity).
A new antibiotic would be held in reserve except in exceptional circumstances. Even if it was put to use on day one for extensively drug resistant TB and the like, there are too few patients to find a functional price point. It's sort of like the situation with many rare diseases.
My favored approach for solving this problem is using some sort of prize system (Sanders had a bill to do this for all drugs last year if you want to see a model). Effectively, the government offers $X billion for a new antibiotic meeting criteria Y and Z, ensuring that the private sector has financial incentive. In most plans, the drug IP would become public, allowing for immediate low cost generics.
And I'm unconvinced its destined to be a commercial failure given Merck is pushing money into it.
Even if something is being used as a "drug of last resort" may have fairly high volume. For example, colistin, which is one of those drugs, are often used in combinations with other antimicrobials to help combat resistance, and is pretty much universally available to hospitals in the U.S.