Resident Evil: Revelations product manager Mike Lunn explains.
When we were developing Revelations for new platforms we really wanted to hone in on the experience you get with a large format screen, surround sound, etc. This type of setup really helps players get sucked into the horror vibe and enjoy the game to its fullest extent.
3DS and PS-vita infrastructure let alone developing games for them are extremely different beasts. Even just the screens as you mention are completely different resolutions/functions.
The game was announced for PS3, Xbox 360, PC and Wii U yesterday, and will see a release in May of this year.