its just a general thing in the US for most death threats not to have anything done about them.
Most death threats aren't illegal in the US because the courts apply standards of plausibility, specificity, and immediacy to them. You can't be charged for posting the NAVY Seal Copypasta at someone because it's implausible, you are not actually a NAVY Seal and you do not have the ability to wipe them the fuck out with precision like you've never seen before. You can't be charged for calling for the deaths of all black people because it's unspecific, your murder boner isn't pointed at an identifiable person but the general category of black people. You can't even be charged for saying a specific person ought to be killed because your ethos that they should be killed is not marked by an intention of action (whether they're a death row prisoner or a celebrity).
To be charged for death threats, at least in theory, you need a mixture of all three. Saying your neighbor should be fed into a pit of lions is specific (neighbor) and immediate (lions), but lacks plausibility. In practice, this is a somewhat subjective judgement and probably is not applied very evenly, leading to the courts trying to not apply it at all. Hence why a lot of these cases are the threats towards Presidents rather than general Americans, because a different standard is applied there.
Or so says my layman's interpretation.
In European laws, the standards I see are based more upon the fear of the victim and the state of the threat's motivation.