In any part of life, if you want to know how to defeat something you have to study it first. It is the only way that you will be able to know its weak points. For example, if a car company wants to know how to stop a certain type of rust from happening on its vehicles then it has to study the rust and see what causes it and how it survives to get bigger. Also, if the medical community wants to know how to defeat a certain virus then again they have to study it and see how it grows and become stronger.
It is the same thing with a computer virus as well. You are not going to learn how to defeat it by just watching the parts of the system if infects. You need to be able to read the insides of it and see what exactly the virus does. You do this by getting a sample virus and opening it up.
Why do I need to do this?
If you are the average person then you do not need to do this. Even if you are running a small business then you are most likely not going to run into this problem as well. But if you are part of a large company who is often the target of black hat hackers, then there is a good chance that you are going to need to do some reverse engineering at some point.
The world of cyber security is different now than it was in the past. There is a lot more money at stake. So there are more black hat hackers now than at any other time in history. Some of these hackers are tired of attacking the same target over and over again. Instead of going after little fish, they want to go after one big target at a time and then get out. So instead of making general use case viruses they are now creating malware that is supposed to attack one specific target.
If that target is your company then you cannot rely on an antivirus maker to solve the problem for you. They have to protect a wide range of consumers and not just one single institution. So instead you will need to hire someone or have someone on staff that can do it for you.
Studying malware and viruses is a helpful way to keep your institution safe.