It's very hard to get the phrasing right. There's always a certain amount of random mutation going on, which can lead to better fitness (or not). However indivi

It's very hard to get the phrasing right. There's always a certain amount of random mutation going on, which can lead to better fitness (or not). However individuals with better fitness end up reproducing more, so mutations that lead to such better outcomes end up surviving. This coupled with multiple ways that bacterias can use to protect themselves against antibiotics, like enzymes, better shielding, or even pumping the antibiotics out, also increases the chance for successful mutations. And they've also developed this mechanism for spreading their DNA around to other bacterias. The result is almost the same as if bacterias would have an agenda. Although it can happen for mutations to lead to worse fitness in contact with older and forgotten antibiotics. And it can also happen for these random mutations to drive a whole population to extinction. But these two outcomes have a much lower probability than bacterias becoming highly resistant to all antibiotics.