The first movie, Raiders of the Lost Ark, came out in 1981. The second movie, Temple of Doom, came out in 1984, and the Last Crusade came out in 1989. These are all reasonably spaced out. However, we didn't get another Indiana Jones movie until Kingdom of the Crystal Skull in 2008, an almost 20 year gap.
Why was there such a long gap between these movies? What led to the decision to pick the series/character back up 20 years later? And lastly, why has it taken almost 7 years to announce the fifth movie?