The things you learn on Wikipedia...

River Phoenix, who played young Indy (aged 13) in Indiana Jones and the Last Crusade, was originally offered the title role in the series [The Young Indiana Jones Chronicles], but turned it down, since he didn't want to return to television. It was originally planned that after The Last Crusade, a second trilogy would be made with Phoenix as the young Indiana Jones and Ford as Henry Jones Sr. (effectively playing his own father). It became increasingly difficult for all parties to fully realize a second trilogy and so a TV series was thought of as the next best thing and a way to test if a prequel set of films could work. However, Phoenix's untimely death in 1993 changed all that.

A long lost trilogy that never made it off the drawing board? And still no part IV? The Goonies sequel will probably get here before another chapter of the Jones saga does.