What do lethal viruses gain from killing people

Viruses are not like bacteria, viruses are not actually living organisms. They are essentially just DNA and protein. They do not "live" off of the organisms they infect, they do not need food to survive. They can self replicate and spread easily from host to host. It is unclear how viruses originated but there is some evidence that they could have been mutated organelles that have evolved. The virus is not striving to survive, it just is what it is. Like a computer virus, it lives to infect.

This is a really interesting question! It is still a great biological debate in the scientific community as to whether viruses are alive or not.

A virus DOES need a host to live, as you said, so killing its host would seem unfavorable. I suppose it's just a completely parasitic relationship: the virus wants nothing but to replicate, and does so until it kills its host. After, it finds another host. I guess it just keeps doing that until it becomes a "super virus"?

Haha idk. I'm stumped. I've marked this as interesting, though, and I'll keep checking back to see what everyone else says! Good question!

same thought as us on the earth , we use the earth to survive but we produce things that harm the host (earth) eventually because we are to successful and over populate we will produce to many harmful things , the virus doesn't mean to kill its host its just a side effect of it living

It is a biological truth that every organisms wants live and reproduce.In this act, hosts get killed. Virus does not really mean to do that.Death of the host is a sequel to its own vital activity.

Nothing. It's the replication and distribution of copies of themselves (to other humans) that benefits them collectively-speaking.
The death of the host is an unfortunate by-product of this.