Why do the words of consecration say “for many” and not “for all"?
There are two dimensions to salvation: the objective and the subjective. The objective dimension refers to the redemption of the whole of mankind wrought by Christ’s death on the cross (see Rom. 8:2, 2 Cor. 5:14). The subjective is the application of the grace of salvation to each individual person.
The current translation of the Roman Missal, “for many,” is a direct translation of the Latin pro multis, and it signifies the subjective dimension. Even though Jesus makes salvation possible for all humanity by redeeming the whole human race (the objective), it doesn’t mean every individual is actually saved (the subjective). God never forces anyone to be saved but allows individuals to exercise their freedom to refuse him. Therefore, the “for many” translation signifies those to whom the grace of salvation won by Christ’s death on the cross has been applied through faith.
The former translation, “for all,” was more of an interpretative formulation that signifies the objective dimension of salvation—that’s to say, the value of Christ’s death on the cross affects the whole human race in that it reunites the human race with God and makes salvation possible. Jesus didn’t die just for a part of mankind but for all (see Rom. 8:2, 2 Cor. 5:14).
Both translations accurately express the different dimensions of salvation. But the Church has decided in favor of a direct translation of the Latin as opposed to an interpretative translation.