Because some people do that kind of thing. It doesn't matter why. What matters is that it happens.
It's better that people with no motive to do harm find these things and tell the people that can fix them.
Sadly, the people that can fix them can't seem to figure out that it's better to fix problems than blame people that find the problems.
The problems that get found ALREADY EXIST. It's not like teh ev1l hax0rs MADE the problem. They just found it. Punishing them for that alone is stupid and counterproductive.
If they do something nefarious with it, that's a different story.
The original definition of "hacker" is someone that takes things apart to see how they work. It's been corrupted into being someone that does bad stuff to computers.
There are a lot of people that can't seem to figure out the difference. That's to bad, because the hackers are the ones that make the Internet better by finding out what parts are flawed so that someone can fix them.
If the software that the hackers find flaws in is open source, they often provide the fix to the people that publish the software along with the security problem.
It seems to me that if someone “takes apart something to see how it works”, and that something does not belong to them personally, or they do not have explicit permission to do so, from the owner, then that someone is in the wrong.