Right, but while these fighters have a short term mind set, the overall popularity of the sport is declining meaning less money overall. Look at Showtimes ratings last year compared to this year. A dramatic drop off. Mainly because of the amount of uninteresting mismatches. If that trend continues, the budget for boxing on SHO will be decreased, and less money to be spread around. In the long run, the mismatches, the ducking, the lame cards hurts the sport and hurts fighters future potential earnings. So that short sightedness of fast easy cash isn't going to help them or the sport.
Additionally Haymon contracts he basically owns the fighter. They cannot sign any promotional contracts, endorsements, do commercials, modeling, etc without his permission (see Keith Thurman rejection of $6m from Roc Nation). By contract, they can't do anything without Haymon's permission.
On top of that, Haymon has already burned a massive bridge with HBO, and it looks like he's burning the Showtime bridge as well. He will have a limited amount of dates on CBS wwhich the venue is a complete unknown at this point. Of he fails, expect a mass exodus of fighters leaving Haymon.