Oh, I don't know, I can see God's glory in His knowing the two coincide.
How would we not know it was a sign from God when it was prophesied beforehand and happened?
From Earth, there are at least two lunar eclipses a year. The book of Joel was written in about 827 B.C. That means there have been almost 5,700 lunar eclipses since he wrote the passage. How many times has the prophecy been uttered that the "Day of the L
ORD" is come, falsely, as it turns out? How many times has that prophecy been uttered, falsely, as a lunar eclipse approaches? I can think of four such cases since I became a Christan a bit over 20 years ago.
Additionally, there has been much speculation that over the next two years, lunar eclipses coincide with the Jewish feasts of Passover and of Sukkot (Feast of Tabernacles). But it isn't the first time that's happened. In fact, similar lunar eclipses in back-to-back years have happened seven times since the time of Christ. Some of those have occurred in years of significance for the Jewish people. One was in 1948 when Israel was granted rebirth as a nation, and again in 1967 when the Six-Day War was fought. Did anything of biblical significance happen then? Well, Israel's rebirth was significant, but it is obvious that is not what Joel prophesied. That event was prophesied by Ezekiel. The war was not prophesied at all, despite war being prophesied for Israel in the Old Testament. Any significant event at any other time in association with a blood-Moon? No.
Will anything of biblical significance happen in the next two years? I can't say for sure. Neither can anyone else. But I do not expect God to act in conjunction with a known celestial event. Though He has put all such events in motion and order, He generally acts in very unexpected ways, such as causing the Sun to pause for a day in the sky, or making it retreat when Hezekiah asked for a sign.
For that reason, I don't believe a lunar eclipse has anything to do with the "blood-Moon" prophecy of Joel. I could be wrong. I believe nonetheless it will be
a complete and total surprise to all of us on Earth, believer or not.