Simply because the English Mass texts we use now are not true translations of the Mass in Latin which is really the “official text”. Many portions of the existing translations do not represent the historic Catholic faith that we have prayed for centuries. You would not want a personal letter sent to you in a foreign language translated incorrectly would you? The English texts we use today were hastily put together in the late 60’s, under a principle called dynamic equivalence. That’s just a fancy way of saying paraphrasing. For example, when the priest says “The Lord be With You”. We will now say “And with your spirit” instead of “And Also With You”. So instead of like saying casually “same to you Father”, we really mean “and also with the spirit that has entered you as a result of your priestly ordination”. That is more theologically correct.