Work life balance does not mean you hate your job, but it is addressing the issue of how much of your time you apply to the ‘work’ thing, and how much time you apply to doing the other stuff that makes you a human being.
If you assume people that are battling with work/life balance hate their jobs, you are coming at it from the wrong direction. I would personally rename it as work/self balance. Yes, I like my job, otherwise I would leave. Currently I hate my commute, but that is a different topic. But ‘work’ and ‘self’ are different things for most people. I enjoy reading historical non-fiction, but for eight hours of every weekday, I cannot do that. If suddenly I started working twelve hour days, it would leave less time for reading historical non-fiction, and that would be sad. Also, I am married, and I have three children. I enjoy spending time with my wife and children. If I spend more time at work, I get less time with family, and that also would be sad. In addition, I like to cook, and I am a pretty competent cook. If I spent more time at work, I would have less opportunity to cook, and my wife would have to spend more time cooking, which would not be fair, and would also be sad.
So lets stop calling it work/life balance, since work is a part of life. Lets call it work/self balance. That seems more accurate.
And if you cannot identify the difference between work and self, well, that is also sad.