Why is it becoming more difficult to treat bacterial infections with antibiotics?

Due to random mutations occurring in bacterial DNA during replication of bacteria, a new strain of resistant bacteria is formed, which is capable of breaking down the antibiotic, so the infection is not cured. As a result, another antibiotic has to be used. But over the years, the number of antibiotics that can cure infections are decreasing due to increased antibiotic resistance from bacteria, and new antibiotics take years to develop, whereas mutations happen much faster. This resistance is as a result of the overprescription of antibiotics.