I think in the case of religious symbols, it’s a case of the influence of Christianity on American culture and worldview. Christianity, of course, teaches that all other gods are “false gods,” so the result is that other religions are de-emphasized and relegated to “mythology,” which essentially translates to “stories that aren’t real” (note that in public school, the Abrahamic religions are not typically taught in the context of “mythology”). Even in non-religious contexts, you can see the influence of Christianity and how it’s still sort of “elevated” above other religions.
This has the effect of turning literally every “pagan” religion into a sort of novelty. You’ve seen it with the aforementioned Buddha decorations. I’ve seen it with my Thor’s hammer. I’ve sure we’ve both seen it with a multitude of other symbols that have been appropriated, whether we realize it or not.