It sounds like a simple question: "What makes you happy?". The truth is that answering this question is not always straightforward.
I like working with people who enjoy their job and do something that "sparks joy" for them. It's important to know what makes a person tick before we can do something with that information.
When we ask this question in an interview, we show interest in a person. The interviewee can then choose to give a personal or professional answer (or both!), whichever they desire.
Whatever the answer someone gives you, it can provide insights into opportunities you hadn't thought of before. For example, the interviewee could be passionate about a framework you've wanted to learn about.
Not everyone is ready for this question
It might sound odd, but not everyone is ready to have a question about their likes thrown at them. I've found that younger people are sometimes scared off a bit, or people have genuinely no idea what to answer.
Ask the question only when in a relaxed environment, and clarify that people are not obligated to answer.
Disclaimer: Passion is not required
Disclaimer to avoid confusion: I do not think people should be passionate about—or like—their job. It's great when people enjoy themselves at work but making it a requirement goes too far as this is a luxury not everyone can afford.
If someone tells me, they need a job to provide for themselves or their family, having food on the table and a roof over their head, that's valid enough motivation for me.