There a number of excellent answers to this question. Here are a few—exploration, description, and explanation; to learn something; to gather evidence; documentation, discovery, and interpretation; the advancement of human knowledge
Here’s a nice one from TheLancet about why medical research is done: "to advance knowledge for the good of society; to improve the health of people worldwide; or to find better ways to treat and prevent disease."
I’m sure you could come up with a few responses to the question yourself.
But I don’t think you would get it, nor do I think the lofty answers I listed above are correct either.
What's the real reason to do research?
To get published.