Knock offs - what am I missing?

I don't think I have ever seen a product with as big and prominent a proliferation of knock offs as Transformers. Obviously things like Rolex and Louis Vuitton purses see a lot of counterfeiting but these are usually sold on street corners and in back alley, hidden stores.
With Transformers I see whole websites dedicated to the selling of counterfeit product. Now I know there is very little Hasbro could do to stop this kind of thing in Asia and such but they could definitely take action against those importing them into the US and selling them online (to people in the US) so why don't they?
I'm sure it would be expensive but that can't be the sole reason, a brand is the most important thing a company has. Are the quality of the KOs high enough that Hasbro isn't worried about the reputation of TFs being tarnished? Are they sold mainly to collectors who know the difference and not to unsuspecting parents thus limiting the amount of complaints Hasbro receives?
With Transformers I see whole websites dedicated to the selling of counterfeit product. Now I know there is very little Hasbro could do to stop this kind of thing in Asia and such but they could definitely take action against those importing them into the US and selling them online (to people in the US) so why don't they?
I'm sure it would be expensive but that can't be the sole reason, a brand is the most important thing a company has. Are the quality of the KOs high enough that Hasbro isn't worried about the reputation of TFs being tarnished? Are they sold mainly to collectors who know the difference and not to unsuspecting parents thus limiting the amount of complaints Hasbro receives?