Why can't I re-install already paid apps?

Hi, I downloaded various apps, including iWork and iLife. These apps have, when un-installed, always been easy to gain access to again for free when re-installed. Until suddenly one day, poof, gone. I have to re-pay if I want them, and they aren't under "purchased". Please help. I have invested at least 40$ in apps, probably more. And I want my products. What can I do?