"American public" wrt space/planetary exploration.

First, the "American public" has no idea of the cost of space exploration. NASA and JPL budgets are utterly opaque to most people, and to the public at large, planetary exploration is hardly an overly costly endeavor.

They do fret -- rightly, in my view -- over lost spacecraft and lost opportunities. These multi-billion dollar losses are of more than passing interest to the public, and they rightly ask "why" such things happen.

Sometimes they find out, sometimes they don't.

Secondly, the public has little or no input into the kind of exploration and research that's done. They might have a greater interest in geology than is generally believed, but if they do, the public has essentially no way to influence the choices made by the space agencies. What happens, instead, is that sometimes elected representatives -- who generally do not discuss these matters in any great detail with the public at large -- are influenced by particular "interests" to advocate certain exploratory efforts and dismiss others. Their advocacy carries much greater weight with the agencies than anything the public may or may not want.

As for the failure of the Vikings to find life: we don't know that. The results of the Viking biology experiments were and are mystifying. It's possible they found some evidence of biology. What they didn't find was definitive proof of biology. Given the way the goalposts were moved during the mission, it's unlikely that the Vikings could have provided that proof in any case.

The reasons why there were no American Mars missions for almost a generation after the Vikings is a story yet to be told. But it wasn't because of public disinterest.