So Jon being sent as a sacrifice because he’s actually really bad at being a princess, except for the getting kidnapped part, and it solves two problems for the kingdom. Think a guard basically standing outside this fearsome dragon’s lair and going, ‘I hope no one kidnaps our princess who is currently unguarded and very much kidnappable.’
Jon’s bitchiness actually working for him and Elias finds him amusing so he decides to keep him. Jon being upset at this at first, but his escape attempts are pretty pathetic. Elias just picks him up and drops him back at his tower each time, like a cat that got out.
Basically Jon gets to be the Dragon’s pet complete with a pretty gold collar.