"Mommy, where do boomboxes come from?"
Well, Darling, when the people of the Netherlands love music very very much, they come up with the brilliant idea of a portable cassette player. Then the Japanese add an AM/FM tuner and improve it's sound and portability, and finally adolescents in the USA integrate it into pop culture!
So maybe that was the most compact history lesson in... history... but that is the true and pretty cool international trajectory that the development of the boombox followed.
Back in the 70s and 80s, bigger was better. Curvy supermodels, muscle cars, big hair, boomboxes, all of it! So when the boombox was introduced to the young urban communities of NYC, LA, and DC in the 70s, it was a hit. The size of the boomboxes gave them a great bass sound that surpassed everything else on the market. Add in the fact that it was portable, and you have yourself a winner.
And then they got bigger... and Bigger... and BIGGER. Not just literally, but culturally as well. As they grew in popularity, more hi-tech features were added, such as input and output jacks for microphones, turntables, and mp3 players (just kidding, this was the 70s-80s). As the capabilities of the boomboxes increased, they became instrumental to many musicians- from music/b-boy battles in the streets to the Beastie Boys having a signature boombox. Not to mention, LL Cool J wrote a love song for the boombox!
Boombox sales began to decrease in the 90s with the popularity of car audio systems and the advent of the Walkman. Furthermore, the Walkman soothed insecurities that other people in the listener's presence might not enjoy the same music. WEIRD. Since there was a panacea for that insecurity, it further enabled it and created an atmosphere of needing a truly personal and portable listening experience.
Whatever, I have no insecurities of blasting this on my boombox in public. You know you like it.