Smurfit Kappa is one of a handful of Ireland’s world-class companies. Now it’s in advanced talks with Atlanta-based WestRock about a potential merger. Why is this happening?  The deal, if it were to go ahead, would create a global giant. Smurfit Kappa is the fifth biggest packaging company in the world by market cap, according to Companies Market Cap. WestRock is the eighth-biggest. The combined market cap would be the second-biggest in the global industry.  Why then are both companies' share prices down somewhat today, on the news that a merger might be on the cards? Deals like these are…