Why do doctors prescribe antibiotics when a person seems to just have a common cold or virus? is it necessary if he has a high fever?

Hard to say: I don't, because it will not help the patient and may set them up for unnecessary side effects. I have challenged some er doctors who seem to do this routinely.Their answer was unexpected. The did not like getting complaint letters to their bosses from irate patients looking for abx. I find it much more likely in settings where there is little or no patient/ doctor relationship.

Pressure: Often the pressure from the patient or their family is so great that the doctor has to worry about disruption of his entire medical practice if he withholds antibiotics from a particular patient, even if they are not indicated. It's a very touchy subject in the medical community.

Normally, physicians: Don't prescribe antibiotics for a common cold or a virus. If the person has a secondary bacterial infection/ complication - then use of antibiotics may be appropriate. A fever could be present with a virus (like influenza) or a bacterial infection. So a fever alone, is not the deciding factor.