At the turn of the 18th century, audience were ready to go over the top, and get some really, really dramatic theater in their lives. Like, a dog dueling a man type of dramatic. In London, only two theaters were licensed, but entertainment entrepreneurs figured out that musical entertainments weren't subject to the same restrictions. So, incidental music was invented, and the melodrama was born. And then switched with another infant. And later tied to train tracks, but rescued at the last minute. And so forth.