Why wouldn't Buck get into his old sled harness?

Buck wouldn't get into his harness or his old spot in line because he intended to take over for Spitz as leader of the pack.

The driver went about his work, and he called to Buck when he was ready to put him in his old place in front of Dave. Buck retreated two or three steps. Francois followed him up, whereupon he again retreated. After some time of this, Francois threw down the club, thinking that Buck feared a thrashing. But Buck was in open revolt. He wanted, not to escape a clubbing, but to have the leadership. It was his by right. He had earned it, and he would not be content with less.

Why did Francois say that buck was worth $

1,000