Because Greek was the language of most of the literate of that era. Hebrew was for the priests primarily.
"If we, in this day and age, can calculate it with complete certainty, then tell me why in antiquity they were so unsure about the exact date..."
You're speaking of the Romish church that rejected prophecy because they rejected Israel, about whom all prophecy was written. If you too reject prophecy in understanding these events, then don't waste my time replying to me. The Lord's apointed times tell all of God's events, to the minute. His word tells us that is what the stars are for; figure it out.
I indeed reject prophecies that spring out of the idiosyncratic interpretations of men and not the consensus of the universal Church, so yes, if you don’t wish to discuss this anymore then I’ll honor your wishes.