Years ago, doctors would prescribe antibiotics for many symptoms of a common cold. today, it is much more difficult to get a prescription. why has the medical industry changed its procedures?

Because we now know that antibiotics can only treat bacterial infections. this includes strep throat and other things such as urinary infections. They won't treat viruses. You can treat the symptoms, but you can not treat the virus. 
(Your doctor will also give you a prescription to prevent infection.)

Bidk