Considering Hawaii's carry law, why do people buy these small pistols. Not trying to be a dick because if we could carry I'd love to have an M&P Shield but for a range gun these seem pretty close to useless.
Well, that depends on your personal situation. In my case:
1. I just got back into shooting after a really long break, and I'm trying out a broad range of gun types, calibers, and manufacturers. .380 is still on my "to do" list. Isn't that what hobbies are for? Trying new things?

2. I usually take my daughters or friends from my office to the range with me. In the hands of a novice, or someone with less hand & wrist strength, a .380 might be manageable whereas a 9mm isn't for some beginners. Case in point, my daughter initially had a tough time with the G26. Her limp-wristing was causing too many misfeeds and FTEs. Same problem with my Sig P226. She improved with practice, but I'm willing to see if the .380 is more to her liking. Of course, the .22 pistols are no problem for her. Just to try another 9mm, I bought a G17 over the holiday. Still need to make it to the range when it opens again to see how she likes it.
3. I travel to locations that allow Constitutional open carry. They also accept non-resident, out-of-state CCW licenses. So, my Maine CCW permit is good in some states I frequent, like NC. Open carry or keeping my gun in the car while driving is okay most times, but it's not ideal when out walking in public.
4. My two daughters also travel. When I think they are ready and capable, I intend to transfer a handgun to each -- probably very soon. Then, if they decide to get a non-resident CCW permit, they will have the option to carry when they travel or not.
5. If you like collecting Glocks, this is another model you just have to buy!

After checking out the SHOT Show reviews, and getting an OGC tweet that 4 are arriving Saturday, I decided to go for it.
My G42 will be our first .380. Whether it's a backup or pocket gun, or just a home defense gun the girls feel comfortable shooting, I'm sure it will have a purpose.
These are my reasons and justifications. If none of this applies to you, or you still don't see the utility in it, that's fine, too.
Now I need to start stocking up on yet ANOTHER caliber of ammo!! :|