The first reason is because back in the 1950s people were still very conservative rock n roll was still popular with teens and most adults and parents hated it.
The second reason is it was a new thing new things either get brushed off or the become the next big thing a big thing was rebellion and teens now and then loved to rebel and rock n roll was how they did that back then.
I know this is probably a stupid answer but it's all I got lol. Hope it helps... somehow