Hi there! :)
This is due to a phenomenon called "Antibiotic resistance in bacteria".
Antibiotic resistance is when bacterias are able to survive and grow in the presence of one or more antibiotics. When this occurs, the resistant bacteria continue to cause infection.
Because of the routine use of antibiotics, bacterial exposure to antibiotics is more frequent and resistance develops at a faster rate.
I'm not sure if this is the answer you were looking for, but I really hope this helped and if there's anything just let me know! :)
