I'm not complaining, just curios. But I've noticed several of my import titles have moderate english. Like Hoshi No Kirby has menus and minigames in Japanese but the powers and levels are all in English. Why mix the two?
I also wonder this splatter house is in full english except ending and title screen
That's even stranger seeing as I don't believe it was released outside Japan.
because it's cool
Hardware limitations were a factor early on. English is simpler to represent in electronic form, its alphabet takes less ROM or RAM then Japanese. Useful for older systems.
But often (like 80sFREAK says) the Japanese just enjoy like toying with English. You'll often see it used in song lyrics or other random places without much practical reason.
In exceptional cases games have had entire English translations created, region coded to only display on English hardware, then released exclusively in Japan. So neither region's users may "officially" encounter the English mode! At least two Game Gear games did this odd scenario. Puyo Puyo and Ronald McDonald in Magical World.