Phil Simms may be right; players may want to play 18 regular-season games (and to earn the money that goes along with that). But the NFL has yet to assume that’s the case.
In the pre-2011 Collective Bargaining Agreement, the NFL had the ability to add up to two regular-season games without any further negotiation with the NFL Players Association. The league surrendered that power as part of the latest CBA (so much for the notion that the NFLPA got nothing of value the last time around). But the NFL emerged from the last round of talks in 2011 the ability to reduce the preseason, whenever it wants.