Because Lucas knows that after a week on Age coming ceremony, his father King Evergreen would announce and give a fief and a noble rank to him and send him away to rule over the fief.
Although it may sound great to get fief and noble rank, but in reality, it was like death sentence to him.
While it is true that every prince would be sent away by the King to their own fief to rule over on age coming ceremony, and this rule/ceremony has been going on for generations.
The previous king also sent away his children to rule their own fief over and the one who ruled the land in best way whether it was economy or military power would be able to become King.
Although this may cause rifts between the children and may lead to bloodshed, the king didn't care as they believed that only the one at the top can really be the king.
The present King became king by walking over his sibling's corpses, he still has his only blood brother who share same mother alive because his brother helped him to get the throne.
King Evergreen was in control over powerful army when he was only prince and his brother was in control over economy, they both were at the top among other siblings.
With his brother's support(money) his was able to build more powerful army and started was against other siblings to get the throne.
Although he won the throne his foundation(army) got severely damaged and the nations power got weak due to this.
It was at this time King Evergreen met with Princess Sofia and then with the help of Princess Sofia, he was able to recover the damaged foundation and also made it further stronger.
And then he married many other noble women to get more funds to build up more power secretly. After death of Princess Sofia, he revealed his ambition to engulf whole Graystone kingdom, but who would have thought that Princess Sofia too builds up power secretly and also left behind few treasures to the King Graystone.
Due to this huge massacre occurred at the border of these two kingdoms and neither of them won.
Well let put aside the past and come back to the present, since Lucas didn't have any background left and was also hated by his brothers, he wouldn't get as many as resources his brothers got.
And not only that as his brothers got help from their mother's side to, but he can get any help from his mother's side since they too hated him for having King's Blood running through hid veins.
And since death of Princess Sofia, the King, Lucas's father hasn't met with Lucas once at all. Seeing this Lucas knew that he couldn't get any help from his father.
To live well and fulfil his parents from two lives' wish and also his wish, he had to became strong and be away from here. But before meeting Chaos stones this thought wasn't possible but now with its help it was possible.
After thinking about this Lucas started to relax a little and took his time in the bath before getting out to get dressed and to have breakfast as his stomach was crying with hunger.