I looked up Shattered Memories on Wikipedia and it seems it came out after Homecoming. Homecoming is available for PS3 so why wasn't Shattered Memories made for PS2 instead of PS3?

Because they wanted to use the Wii's motion control and i'm pretty sure it was before Sony came out with Playstation Move. You could say they were approached by Nintendo, but that's doubtful.

It was a rather long time project planned for the wii.

Here's a few threads that might help you:
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He's asking why it was released on PS2 instead of PS3.

The reason: The PS2 has a larger audience than the PS3 (either regarding survival horror games or just console ownership, forgot which), which is why it was released on the PS2 first: to garner more sales.

The answer's "yes," either way.

There's also the fact that the Wii and PS2 are both Standard Definition and I doubt they wanted to go through all the work of making it HD for the PS3 when the Wii was the version they were focusing on.