I'll wager there are 3 things at play: 1) The sealed restraining order. 2) The warning from f'ing Canada. 3) The rationalization that you'll get in a lot less trouble for being overly cautious than for being overly lenient. Any DA looking at this in a post-Sandy Hook environment goes "white nerd loner with a history of threats attracts attention a country away for threatening schoolchildren." It takes bravery to go "but he clearly didn't mean it, and I'm so confident that I'll take the career blowback if he does shoot up a kindergarten." I'd also wager they'd love to go "get some therapy so we can forget this whole thing" but they can't compel therapy without a guilty verdict. So their choice is "oops, our bad" or "yes we're doubling down on this." A shitty situation all around.