Why do I need a prescription for routine antibiotics in us and not other countries?

Regulation. When people use antibiotics inappropriately (like for "colds" or other non-bacterial causes), it breeds resistant bacteria, aka superbugs that hurt everybody. Other countries are dealing with superbugs now, partly because people are taking antibiotics whenever they feel like it without a prescription. The us is trying to prevent it from getting worse here through regulation of antibiotics.