1. Overuse of antibiotics in non-theraputic settings (e.g. agriculture)
2. Lack of interest in developing new classes of antibiotics
3. Insufficient interest in vaccine development
The last one is particularly interesting because a somewhat-effective vaccine[0] for Neisseria gonorrhoeae was discovered several years ago, but GlaxoSmithKline doesn't want to conduct the trials and submit it for approval until they find one that would be more effective and more profitable for them, so in the meantime it can only be used off-label, which means adoption is next to zero, because most physicians and patients don't even know it's an option. It's also only covered by insurance for its on-label use, which makes it difficult and expensive ($300 for the full series) even for people who want to get it.
Although GSK is at least ahead of Pfizer, who owns the patent for a nearly-identical vaccine that is also shown to be comparably effective against gonorrhea, and as far as I can tell has not even bothered to try using that as the basis for developing another.
[0] about 40%, which for comparison is higher than the effectiveness of the flu vaccine for every year in the past decade except one