I think it's also important to point out that a lot of people became fans of Godzilla not because they thought "hey its a cool social allegory" but because they were kids who saw Godzilla and thought, "hey its a fire-breating dinosaur who fights other monsters!".
Of course, knowing the deeper themes behind the movies helps one appreciate & love the franchise more, but its the inherent appeal to children/families which made Godzilla into a truly lasting cultural icon/cash cow in the 1960s and 1990s.