Had the first invasion happened when Jeremiah delivered these words? Some scholars think yes, some no. Even if Nebuchadnezzar hadn’t yet arrived, he wasn’t far away, and Jeremiah knew what was coming. To a prophet, it was as good as done, and his grief would have been the same either way.
God’s response could be called ‘tough love’:
Jeremiah 11:14 Pray no more for these people, Jeremiah. Do not weep or pray for them, for I will not listen to them when they cry out to me in distress.