Not all piracy ends up to be a lost sale. There are some people out there that pirate, with no intention of purchase. I'm not surprised that Ubi is also finding that F2P users aren't paying either, some people just don't see the value or don't want to spend their money.
Let's take this problem out of the gaming/IT industry altogether. The last time you went to Costco (for non-Americans, it's large warehouse grocery chain), did you see the throngs of people waiting to take whatever free sample was being cooked up? And how many of those people ever actually pay for the real product? Maybe Costco has the conversion rates, but I bet they're wildly unreliable. IMHO, what I tend to see are a bunch of freeloaders who will take anything that is free and then leave when the offer is made to purchase the product.
Free-to-play, free-to-sample, it's all the same thing.