I think the idea was not to make the crew suspicious that it was a trap by making them have to work to retrieve B-4. They wouldn't suspect a Trojan Horse if they thought it was something abandoned that they needed to unearth.
Oh, I understand the intent. But it still doesn't make sense to hide B4 on Kolarus (see next.)
Well, I'd hardly say "sure to," because B-4's parts were in a remote area and it was quite a while before the Kolarans arrived. With a little more luck, they could've been in and out before anyone came to investigate.
But again, why even have the remotest chance that Picard could come to danger? Why not just bury B4 on an uninhabited planet? Shinzon needed Picard's blood to survive. If I needed someone's blood to survive, the last thing I'd do is send that person on some wild goose-chase where there's even a small possibility that said person could be hurt or killed.
(I know, I know: You can't have an action-pack'd car chase on an uninhabited planet

)