You're hearing "why" but what's being asked is "what"
A helpful post for job seekers:
You're hearing why, but the question is actually "what"
Common interview question: "Why do you want to work here?"
The question that's really being asked (most often): "What about us played a major factor in your decision to apply to work here?"
The two questions are substantially different.
“Why” questions are "judgment questions." They invite you, the interviewee to reflect on your judgments. They're hard questions to answer because who likes to question themselves. They're also hard because it's easy to overshare.
“What” questions are easier to answer. "Why is the sky blue" vs "What happens in our eye to cause us to perceive the sky as blue".
Here's a framework you can use for prep'ing for that question.
Demonstrate you know a bit about the company. Try to understand how they make money, their customer, and read reviews and news.
Review the job description and look for VERBS. Why verbs? Because verbs are actions. "What do you want to do with your life?" is basically, "What are the verbs you want your life to be about?" So read the job description for verbs. Are these the verbs you want to be doing at work?
Research the hiring manager if you can. Are these people you want to work for? Read their content if they post here. Does it appeal to you?
Here's a framework for answering the question.
When I decided to apply for ____, it was important for me to consider these factors a, b, and c. After researching your company, it's clear I can achieve "a" through _____ (insert relevant detail about company), "b" through ______ (insert relevant detail), and "c" through _____(you know what to put here).
What's the outcome you want?
Give confidence to the person on the other end that you know what's important to you, that you believe their company will help you do those things, and that you will create value for them.