That's a tempting way to look at it. "Don't want to enable ads? I don't want you wasting my bandwidth!" However, outside of rich multimedia or unusually popular

That's a tempting way to look at it. "Don't want to enable ads? I don't want you wasting my bandwidth!" However, outside of rich multimedia or unusually popular content, the marginal cost of serving a page view is peanuts compared to the hours (or days, or months) of human labor that already went into producing the content. Since creating quality content is the part that's difficult and expensive, it stands to reason that it's the part that should be monetized. It's really an accident of history that content creation was able to be subsidized by advertising or charging for distribution.