I saw a model kit that caught my eye, Aoshima's 1/700 JMSDF Missile Craft Hayabusa/Umitaka kit. It looks like a handsome boat but was curious why such a small boat was $24 so I looked it up. It turns out that there are actually 4 models in this kit. There are 2 missile boats and 2 P-3s in the kit. Why can't I just buy 1 missile boat for $10. Are these 2 pack kits annoying anyone else?

They probably do that because packaging and marketing are just as expensive for one model/box as for multiple models/box actually making it cheaper for the consumer (you) in the long run. So now you can build a fleet!

It's not uncommon for JMSDF ship kits to include more than one model in them. Usually related support craft or other smaller vessels are packaged with them. For how small the ships are to begin with, it makes more sense from an economical standpoint for both the manufacturer and the consumer to package them together just as Biggles pointed out.