The former players wanted a deal for $$ right away. The NFL wanted to make the story go away. The initial settlement was paltry to begin with, and both sides knew it.
I get the desperation from some factions within the vets group (need money for treatment NOW), but if the amounts paid out initially (using the scale that was part of the deal) are going to basically drain the whole fund, it doesn't make sense for the group as a whole. In that case, there's just going to be an even larger group of desperate vets in 5-10 years.