“If you control an artifact creature, a nonartifact creature, and no other artifacts or creatures, you must sacrifice both permanents. You must choose the artifact creature as the artifact and the nonartifact creature as the creature. The same is true for any combination of types—you sacrifice a number of permanents as close to five as possible.”

What is the reasoning for the last part of this ruling? I can seem to find anything in the comprehensive rules that would state that this is true, apart from the fact that we would have to apply the effects in order. Would this outcome be the same if I controlled a Creature and an Enchantment Creature and no other permanents aside from lands? Since Release specifically mentions Creature before Enchantment, can I simply chose my Enchantment Creature as my choice for my Creature selection and therefore not have a target for Enchantment, or will both still need to be sacrificed regardless? If both have to be sacrificed, what is the correct reasoning for this? I feel like I'm missing something completely and blatantly obvious here and over examining it.