The Guardians knew how long Jack had spent alone. Of course they did. But for someone who had lived as long as Bunny or Sandy, or someone who could get caught up in their work to the point of having a week pass by without their notice, like North or Tooth (or, to be fair, also Bunny) it was much more difficult to register just how difficult those three hundred years would have been for someone like Jack, who craved interaction with other people the way a fish craves water.
And, though the Guardians hadn't noticed, spirits had been growing fewer. Oh, people still believed in things, it was true, otherwise the Guardians themselves would have had to notice. But new spirits, oh no. They looked to other explanations, didn't create new spirits unless in fun now.
They might be created – look at Slenderman, or O'SHA – but it wasn't belief like was needed to sustain a spirit. Most of the ones that did appear were brief and weak as belief waxed and waned.
A Weather Phenom like Jack Frost? Even rarer. With radar, and storm tracking, and all the rest...why believe in a spirit causing the weather when everyone knew it was because of shifts in air pressure and warm air versus cold and all the rest? Jack was lucky in being old enough and embedded enough in culture that his name was still spoken, and he was strong on his own, from being raised by the moon and his own inner strength, that direct belief didn't weaken him.
Most all other Weather Phenoms had drifted away into nothing but a voice on the wind, fading away into nothing, as the years passed. New spirits were rarer and rarer, and the older spirits so entrenched in what they did that they didn't have time for a carefree spirit like Jack.
He irritated them at best. At worst, well, Jack was probably lucky he hadn't gotten into more fights than he had.
Three hundred years of being rejected. Of thinking he'd found someone only for them to fade away soon after. Thor and Loki were lucky, pop culture along with modern paganism had revived talk of them, and stories were still told of Raven and Anansi, while the play starring Puck was part of mainstream consciousness. The Snegurochka were less lucky – the stories were still around, but not well known, and they had never been powerful.
They were lucky in finding Jack, and having him supporting them, unconsciously as he did. Without him, they would have been even weaker, easy prey still for any spirit stronger than them, which was nearly all of them.
Snow Maidens and Little Match Girls (many of whom Jack had changed to Snow Maidens – even as weak as a Snow Maiden was, they were more powerful, healthier, happier than the misery of a Little match Girl) didn't last long in the service of spirits like General Winter or the Snow Queen.
But Jack was strong enough, loyal enough, and the Snegurochka weak enough, that no one fought him for them.
And they were all upset about Jack's upset, about Jack being lied to, and though they were weak they could make life very unpleasant for another spirit if that spirit hurt Jack more.
As shovel talks went, the diversion from stories about Jack to the Snegurochka's weren't very intimidating. The worst most of them could do was frostnip, maybe frostbite, which wouldn't harm a spirit for long though it would be painful. And while they might be a little jealous of the baby teeth, Baby Tooth in particular, they weren't going to harm any of them.
None of the snow maidens said it, but there was that secret hope they shared that Bunny could feel and wouldn't breathe a word of either, that the baby teeth could be their sisters as well. That they could love and be loved too, if only for Jack.