I believe that Easy-jets support of R3 is because it would cause such chaos at Lhr that it would benefit them at their home base viz BA.
I am sure WW must be thinking the same, just think the tearing up of the M25 would make access to T5 very difficult for a number of years. The M25 is regularly gridlocked now, and even when finished the increased traffic flow on the M4/M25 would lead to major headaches