Not always a bike. Sometimes just a trolley or a handcart or a custom jerry-rigged contraption.
Okay, in all seriousness: boom boxes were a thing in the 1970s and early 1980s. There are still people who use the latest generation of them, but thankfully not nearly as many. These days people cranking music in a public place are generally doing it as part of a group that all want to hear the same thing. (and in back then the group wanting to hear the same music was the common case)
Second is probably motorcycles blasting it over the engine noise.