"Traditionally, if you produce something of value, people will pay for it" but if there's better value elsewhere that's where they'll go. In this case the best value of all is FREE ie no flattr account.
Hopefully it will reach a critical mass sufficient to allow sites to REQUIRE a flattr account to see their content. Note that this is different from requiring a subscription, since you aren't forced into donating to them. But you are forced into jumping into the 'donation scheme' so if they produce content you like, why not click it?
I'm not sure what kind of critical mass that would require though. I think in some niche areas it would be possible without much effort if there was some sort of banding together among the major content producers for that niche.
