Why are anti viral drugs only used for life threatening viruses?
Viruses use a cell’s own machinery to reproduce[1]. Antibiotics target bacteria and not viruses[1]. Anti-viral medications and vaccines can disrupt the reproductive cycle of the virus[2]. 
Antiviral agents do not actually kill the virus itself, but rather inhibit its replication to prevent it from increasing to a point where it could cause pathogenesis, allowing the body's innate immune mechanisms to neutralize the virus. [1] Developing antiviral drugs is difficult due to the quickly evolving characteristic of viruses and the ability for many viruses, like HIV and papillomavirus, to enter a sleeping mode wherein the infected cells do not produce any new viruses. [3] In order for an antiviral drug to be used, the virus species that is targeted must be a serious threat to public health and wellbeing. [2]