Answer: Some pathogens became resistant to the antibiotics.
Step-by-step explanation:
The main problem that developed because of the use of antibiotics is development of antibiotic resistant organism.
The frequent use of antibiotic on the pathogens caused mutation in their genetic material and they became resistant to it.
As a result of this there was no effect of using antibiotics on such pathogens. Due to this reason the disease remained in the body for a longer period of time and it is not cured.