I'd also speculate that it has a lot to do with Trump's willingness to work with Russia and Assad, as opposed to Clinton's opposition of both. There are a lot of factors at play when a sovereign of a state backs a candidate in another race, but it has almost nothing to do with the party that the person is affiliated with, or even the person running (as SA's historical bipartisan funding of both parties shows). It's about which candidate is perceived to serve Saudi interests better than the other. For a wide variety of reasons, this election year, that candidate is clearly Clinton. But that doesn't amount to anything like Clinton tacitly approving of Isis. It might mean that the Saudis prefer Clinton over Trump because a Clinton presidency is one in which the rebels will be backed against Assad (Saudis are regional superpowers, they have their own motives). But the issues shouldn't be conflated.
You also have a habit of posting the conclusions of a given author as being some kind of unbiased summary. Usually, in the links you've posted, the author has a motive which is so obviously transparent before the evidence of source material is ever introduced.
Just to finish up. Why doesn't the media report on this? Probably for the same reasons that the mainstream American media has avoided highlighting the various controversies surrounding US allies for years. Self interest, narrowness of platform, and limited scope in terms of discourse.