BCP stops after the last "1000 rows sent to SQL Server. Total sent: ..."
After 3 hours, I finally got my prompt back:

55837 rows copied.
Network packet size (bytes): 4096
Clock Time (ms.) Total     : 10582641 Average : (5.28 rows per sec.)


Although I still don't know why it didn't return immediately since the rows were already inserted. My best guess was it did index rebuilding.

I will try terminating the console the next time it hangs up like that.