I think that question is too simple.

1. We might not be the only hosts or place where it can survive. Measles seems to have mutated from a cattle virus.

2. Killing the host might be the virus' end-game, in which case it evolved to extinction. Mutations nor evolution don't have a goal. There's not always an advantage. I bet most changes aren't advantageous.

3. If you really want to see everything in terms of evolutionary change, the virus could even been seen as a tool in human evolution.

Evolution is a way to look at changes in and forces operating on living things. It is a property that emerges for human observers. Nature doesn't care about it.