The really big problem for Selleck was how the timing worked out - CBS, naturally, would have had no problem having Selleck star in the picture under normal circumstances. Who wouldn’t want the star of their upcoming series to be the lead in a major motion picture? It’s great publicity.

The problem was that Magnum P.I. was developed for a specific purpose - to make use of the sets and production equipment left in Hawaii from the filming of the long-running series Hawaii 5-0.
Therefore, since that series was still filming until the beginning of 1980, CBS could not film Magnum P.I. any earlier than early 1980, which directly conflicted with the March 1980 filming schedule for Raiders of the Lost Ark.

Thus, CBS told Selleck he could not do the film.

That’s fairly well known, but what’s a bit less well known is that, as it turned out, there was a television writer’s strike in the Spring of 1980 that halted production of Magnum P.I. long enough that production was delayed for a few months, giving Selleck plenty of time to do Raiders of the Lost Ark…if it hadn’t already been given to another actor.

Pretty sad.

As a cute gag, in one of the very last episodes of Magnum P.I. ever made, Selleck was finally given the chance to play Indiana Jones, with “The Legend of the Lost Art.”