Backstabbing is pretty common so I am not surprised that it happened between PMS and Crunch, ultimately every players dream in Tribal wars is Victory and they don't care if they need to shit on the players face or not, btw not all players tolerate backstabbing there are a few players who are decent and still want to play fairly.
Crunch just want to win, thats it. Players of PMS are frustrated after all the support they have sent, all the nukes they have sent all the planning. PMS giving the opportunity of a united front against Cicada eventually Cicada conceding defeat, PMS fighting tooth and nail against SINTM, PMS not collaborating with SINTM against Crunch, where as eventually Crunch just decided to backstab.
Of course, Crunch will justify their moves with flowery remarks and will eventually blame PMS leadership, I think they will also say that PMS tried to backstab Crunch first.
Btw, no one is fooled Crunch leadership and top players of their tribe already talked to players of Cicada in giving them villages. When you take a bribe be sure to give due.
In reality Cicada succeeded in playing the ultimate card. Give victory to someone who doesn't deserve it.