So Rafael Brandão sent me this tip and some screenshots. Apparently many, many songs on thesixtyone.com aren't getting any hearts at all. And there's no way to direct message the artists to tell them someone will stumble upon their tracks ... eventually.
As to the artists and listeners who put time and money into building up the site? T61 admin James Miao is still standing by his statement, "Just because you like my stuff doesn't mean I owe you anything."
Three (of many) pages of unhearted songs (click for big):