I'm not a doctor or biologist, but remember that bacteria is a far simpler organism with a much shorter individual lifespan than a human. Depending on the species and their environment, they might divide every 12 minutes or every 24 hours. A new human generation will be more 15 to 35 years. Their reproduction is also simpler. Genes are inherited or mutated mostly at the time of reproduction. Selection is mostly therefore over the course of generations.

These things together mean their microevolution is on a different timescale than ours.