Probably the most important is family. I currently live no more than four hours away from all of my brothers and sisters. My parents live close enough that we go to church together, share a meal at least once a week, and do some sort of weekly exercise together at least once a week. My children see most of their cousins (from both sides of the family even) on a relatively regular basis.
The same is true for friends. While we have still have friends in Alaska, few of them live near each other and we now have decades of time separating us. Chances are also small that I will be able to get a job near where any of them are due to limited teaching opportunities in the more populated areas of Alaska. Meanwhile, our friends here are amazing. They have been supportive, helpful, and entertaining in ways that I had never thought possible.
Alaska is isolated. While the isolation is part of Alaska's call for me, it also means that many things are more expensive, and some aren't available at all. If not in one of the main metropolitan areas, you have to rely on shipping for a number of products, and shipping to Alaska is more expensive.
For that matter, almost everything is more expensive. While this is slightly offset by the fact that there are no state taxes (and even a permanent fund dividend after living there for a year), costs are simply higher for homes and many groceries. This also includes travelling to anywhere outside of Alaska, which we would want to do to see family.
So far, these negatives (as well as the normal problems of finding a job and a place to live) have been enough to keep us from moving back.