Why did viruses evolve in the first place?
The are different theories about virus evolution, some speculate that they were evolved before the cells, some speculate they are evolved to spread genetic information, a sort of specialized conjugative pilus others say that they are cellular parasites. Still, none has the final answer yet, but thanks to the boost of DNA sequencing, many new pieces of the puzzle come out lately so keep updating your knowledge! 

Whether they are alive or not is also matter of discussion and it pretty much depends on the definition of life itself.
If you define life as the property of reproducing, transmitting genetic information and evolve, then viruses are life forms. But if you want to include in the definition that a life form must have all the biomolecular machinery encoded in the DNA (I really disagree on this point), then they are not. To me, they look quite a living thing.

About your sentence: 


  So what's the point of all this? Infecting the host and causing so
  much trouble for the host...


I think you are looking only at the "negative" side. Viruses can transfer useful genetic information, plus they are involved with the evolution itself. We humans have lot's of viral DNA in our genome, so no viruses, no humans as we know them. Think about it ;)

There are plenty of resources around to get a better insight please have look at the following links to get started.

https://en.wikipedia.org/wiki/Viral_evolution

https://en.wikipedia.org/wiki/Evolution_of_influenza

http://www.sciencedirect.com/science/article/pii/S0042682215000859

https://link.springer.com/article/10.1007/s00239-013-9601-0

https://www.nature.com/search?order=relevance&amp;q=evolution%20of%20viruses