Instead of saying that people dont know their history... (I made a lil research)
The roots of hip hop music are in West African and African American music. The griots of West Africa are a group of traveling singers and poets, whose musical style is reminiscent of hip hop. True hip hop arose during the 1970s when block parties became common in New York City, especially in the Bronx. Block parties were usually accompanied by music, especially funk and soul music. The early DJs at block parties began isolating the percussion breaks to hit songs, realizing that these were the most danceable and entertaining parts; this technique was then common in Jamaica (see dub music) and had spread via the substantial Jamaican immigrant community in New York City, especially the godfather of hip hop, DJ Kool Herc. Dub had arisen in Jamaica due to the influence of American sailors and radio stations playing R&B. Large sound systems were set up to accommodate poor Jamaicans, who couldn't afford to buy records, and dub developed at the sound systems (refers to both the system and the parties that evolved around them).
Herc was one of the most popular DJs in early 70s New York, and he quickly switched from using reggae records to funk, rock and, later, disco, since the New York audience did not particularly like reggae. Because the percussive breaks were generally short, Herc and other DJs began extending them using an audio mixer and two records. Mixing and scratching techniques eventually developed along with the breaks. (The same techniques contributed to the popularization of remixes.)
As in dub, performers began speaking while the music played; these were originally called MCs; Herc focused primarily on DJing, and began working with two MCs, Coke La Rock and Clark Kent—this was the first emcee crew, Kool Herc & the Herculoids. Originally, these early rappers focused on introducing themselves and others in the audience (the origin of the still common practice of "shouting out" on hip hop records). These early performers often emceed for hours at a time, with some improvisation and a simple four-count beat, along with a basic chorus to allow the performer to gather his thoughts Later, the MCs incorporating brief rhymes
These early raps incorporated similar rhyming lyrics from African American culture, such as the dozens. While Kool Herc & the Herculoids were the first hip hoppers to gain major fame in New York, more emcee teams quickly sprouted up. Frequently, these were collaborations between former gang members, such as Afrika Bambaataa's Universal Zulu Nation (now a large, international organization). During the early 1970s, breakdancing arose during block parties.
now... If you listen to 50s rock and today's rock... it did evolve (think Elvis and Metallica)
if you listen to RnB... same thing (think The Commodores and Boys to Men)
Country... same thing
Jazz... same thing
All music styles are evolving... even classical music evolved...
Why would Hiphop be the only one not to?