Why are polyunsaturated and monounsaturated fats at a zero goal when they are healthy fats

What Alatariel said, plus a further comment about the reason there is no set goal: MFP doesn't just make up goals. They base them on recommendations from mainstream nutritional experts, often on US government nutritional recommendations.

Loosely speaking, the US guidelines are to get good amounts of the unsaturated fats up to your fat intake requirements, but to limit saturated fats, but there's no numeric recommendation from the government for the unsaturated fats. Therefore, MFP didn't make up a goal, they set them to zero.

By doing that, they allow you to set those goals numerically to anything you think is a good value, in context of your own nutritional needs.

Personally, I haven't bothered to set a goal. When I look at the unsaturated fats on my nutrition page, if the day's totals are negative, I know I ate some, in one sense the more the better as long as I got all other needed nutrition. I treat the saturated fat goal roughly as a limit, trying to stay under or at least near it most of the time. YMMV.