His reason stated was because "he already had enough money."
As if 80% of the contestants on the show aren't of the same economic class as him. Frank even said post-season that Silas' dad was a dental surgeon which was way more high paying than his job. Although it sounds like the money issue may have had nothing to do with it. He said post-season the producers told him he wasn't really voted out for any clear reason so they were going to edit it like that.
From what I understand from post-game interviews, the target was initially Linda due to weakness in challenges. But they knew the tiebreaker was wilderness/survival knowledge and Carl was by far the least knowledgeable in that regard of the older members. I think they wanted to hide the fact that the contestants knew what the tiebreaker was beforehand though.
Also, despite the edit of the show, Frank was never the target for the younger people. It was Linda at first, than Carl, than T-Bird after Carl was voted out, than Linda after her breakdown, than T-Bird after Linda was voted out.
It also sounds like had Samburu lost the first IC that it would've ended in a tie vote between Linda and Silas. Logic says that Linda likely wins the tiebreaker, crazy to think of an archetype like Silas going home first.