I don't really know why it's so small but it is an indicator of how little is done with it. You're not prompted to install so I'm guessing it's just randomly accessed whenever it's needed. There are still "now loading" screens from time to time.
Or it's probably just a requirement and has nothing to do with installing. I've decided to take a break from playing. I get sooo addicted while I'm in the game sitting straight through 4 hours or more. The cutscenes in particular really draw my attention because of how fluid some of the movements are and for once we have proper mouth movements to fit the english voiceover.
One weird thing to note about the sound is that in some areas or battles, there's a lot of 'echoey' effects when it comes to voices or sound effects where there shouldn't be any.
I guess you don't realize how small 500kb is, it's not even enough space for one music file