Fairtrade Cocoa: Shouldn't All Chocolate be Fairtrade?

I was just reading an article on confectionerynews.com  which says that there is enough fairtrade for more of the bigger chocolate brands to convert to fairtrade cocoa.

So why don't they?  

Is it too much to ask for the cocoa farmers to be paid a fair price for their labour?

Consumers need to put more pressure on chocolate manufacturers to use ethically sourced ingredients.