Another reason is that you have to realize how much of a minority of players actually use the forums. Without looking at the actual numbers and guessing from the top of my head, I would say less than 5% of our subscribers use the forums regularly. Keep in mind that even less than that % would even answer the poll. That is a pretty tiny group of folks to let make actionable decisions on, which is why we use a lot of facets of data (including the forums) to make decisions, and not them alone.
This alone should be enough to answer the people who complain that suggestions are never acted on.