Why doesn't the four-gluon vertex give mass to gluons? We have a four-gluon vertex and a gluon vacuum condensate. Why doesn't this provide us with gluon masses, as in the NJL model where the condensate gives rise to an effective mass term?
 A: Well, in the NJL model you get rid of the gluon. They are considered to be frozen in the low energy limit where you are working because the mass is higher than the energy. Thus you are only working with quarks, and you consider interaction between quarks via effective coupling constants.
But in the standard model, gluons (seem to) acquire an effective mass because of confinement. That's why the range of the strong interaction is short.
If you compare with photons, they  have no electric charge and the range of the electromagnetic force is infinite.
A: As stated by @JSFdude, in the NJL model, gluons are no more: they are replaced by the effective 4-fermion couplings. 
That said, ab initio QCD calculations DO indicate that gluons could acquire non-zero mass. A recent paper claims:

Preliminary variational calculations[31–33] had shown that PT
  might actually work at low energy and give reasonable results at the lowest orders of approximation if the expansion point is changed and the expansion is taken around a
  massive gluon propagator. Regardless of the accuracy of
  the zeroth order gluon propagator, provided that it has
  a mass scale, the higher-order terms become small, suggesting that the failure of PT might be a consequence of
  the bad choice of expanding around the usual mass-less
  gluon propagator of the high energy theory. On the other
  hand, the even earlier remarkable discovery of Tissier and
  Wschebor[44, 45], that PT is viable if a gluon mass is
  added by hand to the Lagrangian, suggested that the best
  expansion point might actually be the simple free massive
  gluon which emerges by just adding a gluon mass term
  to the quadratic part of the Lagrangian and subtracting it again from the interaction, thus leaving the total
  action unchanged.

where PT stands for perturbation theory.
Of course, the rigorous proof of "The mass of the least massive particle of the force field predicted by the theory is strictly positive" is still pending with a prize of US\$1,000,000. In comparison, a Lamborghini can start anywhere from \$200,000 to \$500,000. So I am not particularly enthusiastic in telling ya the proof here at PSE. 
