Food, shopping, areas to relax. Plus, it's easy to get out of the airport and
catch a train into town very quickly. If I have a long layover in Amsterdam, I can get into downtown almost always within 40 - 50 minutes of landing. Getting out and through customs is easy.
Getting back into the airport...that has turned into an arduous process. It used to take less than 30 minutes to get back into the airport if you did not have to check bags. Now it takes at least an hour the last few times I have done so.