Or do you think that way because you've always assumed it was a problem? It isn't until our most insecure moments of adolescence that we really start sweating enough to require deodorants. What better time to strike at insecurities to sell a product for life? And after all these years, it certainly is a reinforcing loop. for example, you don't see ads trying to convince you that body odor is an issue - that's assumed.

Not that I disagree with you, I think that the mix of increased population density in cities combined with chemistry made it all but inevitable. But the cynic in me finds the idea of self propagating ad campaigns brilliant.