Every situation and person is different. It's impossible to say what combination of factors motivate a guy, or if there is even only one main motivator. Some guys want to get to the league as quickly as possible. I'm sure some guys do feel a loyalty to the 1 out of 31 teams that drafted them instead of 100s of other options. Some want a team that has a track record of good development. Some want to be in a hockey market. Some don't want to be in one so they aren't hassled all the time. Some want nice warm weather. Others might prefer a cold climate they've always lived in. Some may want to be near friends, family, former teammates, coaches, whatever. And it goes on and on.
The teams and all the different players and coaches they interact with for years have to just hope they learn a little bit about what makes them tick and make the right moves to get them in the fold. It's the real life version of the old NCAA football recruiting mini games. At the end of the day, these are 18-22 year olds, and they can have so many different priorities, and they are prone to changing in an instant. Sometimes, you may do everything right like in a Fox situation, and there's just some factor out there that is impossible to overcome. Probably another reason why having as many darts as possible is the best strategy.