Unhealthy food tastes better than genuinely healthy food because the three components that can make food "unhealthy" (salty, sugary, and fatty) were rare back during our days as hunter-gatherers. We like those tastes so that when we found them, we would remember where we found them.
As we became more agricultural, some of these components could be accessed more easily. They became even more accessible as humans industrialized, and eventually became much more common than thousands of years ago. That's why there can be so many unhealthy foods that we constantly want to eat.