As with this map here, the reason why they inset Alaska (and Hawaii) is purely because of their geographic location in relation to the rest of "mainland" USA. If they were expand the map (to scale) to include Alaska and Hawaii without insetting them there would be lots of "irrelevant" space within the map. Instead, they inset these areas as to avoid that happening.
why is the inset map of north america included
why is the inset map of north america included
The location in relation 2 the mainland