A new musical subject..?

"Political or social issues can still be addressed and remain relevant, either in the historical context or the more general way that the characters deal with eternal situations."

This is true, but isn't the issue being explored to do with whether such issues can be the main subject matter rather than just an underlying theme?

Take the "boy meets girl" plot and the "good versus bad" plot, and you can place it within any "issue". Base those two plots within the French Revolution, and you've got "Les Mis", base them within Christian history and you've got "Jesus Christ Superstar", base them around man-eating plants and you've got "Little Shop of Horrors".

People don't leave the theatre after seeing Les Mis and scream "Down with the French Aristocracy!". They usually comment on the costumes and music, have a nice tall latte and go home.

None of these musicals are exploring issues. The issues just add colour to typical plots.

So why aren't there more musicals with such issues as their main subject?

Sondheim did the political "Assassins" as well as the melodramatic "Sweeny". Which one is staged more often?