FD have been saying right from the start of alpha that they hope there will be a wipe for gamma (which they are now calling the preview) but providing there are no problems your progress in gamma will carry over into the release version.
As for backers getting rewarded, we got plenty of rewards including things like extra starting options, the chance to help shape the game, or even at the most basic level a simple discount for pre ordering.
If you expected to keep your progress all the way through from testing I suspect you haven't had much involvement with beta testing games in the past, usually the testing phases are balanced to allow parts to be tested and not to make the full game fun, starting with a whole heap of credits that were far easier to earn than they will be in the real game is a huge waste of the game.