Like the people who made Oregon Trail DSiWare might not have permission to renew it for an eShop release.
Or something. It's possible Gameloft may be planning on a 3DS specific version of Oregon trail. Let's Golf isn't transferrable but there is a Let's Golf 3D on the way for eShop.
There's only like 11 games you can't get (supposedly Domo and Pinball Pulse will be coming soon). The Browser didn't need to be transferred, Flipnote is coming in 3D anyway, Gameloft will most likely put out Real Soccer 2011, and someone else is in charge of the Sudoku games from Nikoli now.
http://www.digitalnintendo.com - Find out what's out, where it's out, when it came out and more between Wii Shop, DSi Shop, and eShop!