160m FT8 RX overnight with the earth-electrode "antenna" in the ground

After being spotted by 31 stations with my 2.5W 160m FT8 last evening, I was RX only on 160m FT8 overnight. Over 400 stations spotted (see map). Fewer than a few days ago, but still plenty.

I am amazed how well this "antenna" works on 160m and 80m QRP. Why go to all the trouble of a big eyesore antenna if something this simple works?  

I may give this setup a test on 80m SSB next Sunday in the CDARC net.