In the Young Wizards/The Book of Night with Moon universe, the Lone Power seems to like killing off the protagonists' family members to try and push them over the Despair Event Horizon or make them desperate enough to cut a Deal with the Devil. The protagonists cannot possibly be the only ones this has happened to. For that matter, It has been known to extinguish stars to hinder the protagonists, killing off entire civilizations in the process. Once again, It's probably not giving the protagonists special treatment here.
It doesn't help in the least that it is made explicit that there is an afterlife, and it's a much nicer place. Hello Unfortunate Implications on the morality of keeping somebody alive in that universe...
Nita and Kit's joint Ordeal ... well, as Nita herself puts it in High Wizardry: "If we'd copped out (...), this whole world would be different. And believe me, you wouldn't have liked the difference." Are all Ordeals that important? And if so, is the world one preteen kid away from disaster at any moment?
"Some of those kids are out on their Ordeal ... and because they don't have time to become good with the Speech, they get in trouble with the Lone Power that they can't get out of. And they never come back."
If a given wizard or group of wizards cop out or fail their Ordeal, another wizard or group of wizards, on Ordeal or otherwise, receive the task of cleaning up after them, or helping them through the Ordeal. For example, A Wizard Alone.
also Nita and Kit were somewhat younger then most wizards when they started, thus had more power, and a more dangerous Ordeal. Dairine was even younger and her Ordeal was even more universe-changing.