Tin Pan Alley was the district of New York where sheet music was published in the late-19th/ early-20th century United States. These songs survive and even thrive today either because they are so popular that they're saturated into American society, or also because their copyrights have all expired so they're public domain. "Take Me Out To The Ballgame" (1908) and "God Bless America" (1918) are Tin Pan Alley songs. And have you ever watched a cartoon, especially Warner Brothers cartoons from the 1940s, '50s, and '60s? The background music in hundreds of these cartoons samples "The Sidewalks of New York," "Hello! Ma Baby," "Give My Regards To Broadway," "Yes, We Have No Bananas," "Ain't She Sweet" - the list goes on forever. And don't get us started on I Love Lucy reruns! These songs have been around for about a century now, and they're so saturated into the Western consciousness that most of us aren't even aware of how many we know by heart. . .http://www.songfacts.com/blog/writing/what_the_heck_is_mathcore_your_guide_to_obscure_niche_genres/