Well, not always. I know guys who had fights cancelled when they had done full ( already paid ) pre fight camps done and this cost money and health ( a lot ). If you do not fight you lost interest about you with time and in general sponsors and promoters are interested in you if you fight more often and are popular. I even know case when supposed opponent's promoter and manager had expressed in public media that they are ready to pay sum x for fight vs guy while in reality when it is time to sign contract, after almost 2 months long talks appears that they had offered in contract 4X lesser fight purse. I will not mention fighters names here but this is stuff done by PIGS not humans.