A massive shot across the bow of Sony to get them to shut up, most likely.
http://www.nintendoworldreport.com/news/62314/microsoft-announces-ten-year-agreement-to-bring-call-of-duty-to-nintendo-systems-if-activision-acquisition-completes
If the contentious Microsoft acquisition of Activision Blizzard King goes through, Nintendo players will directly benefit according to an announcement from Microsoft gaming head Phil Spencer.
Overnight, Spencer announced in a social media post that Microsoft has signed a deal with Nintendo that will see North America's most popular console game franchise come to "Nintendo platforms" for ten years. As the deal is not approved by regulators yet, details of what form this would take - ports of prior games, the popular free-to-play Warzone running on Switch in some fashion, cloud streaming, or the newest games running on a potential Switch successor - cannot be confirmed.
"Microsoft has entered into a 10-year commitment to bring Call of Duty to @Nintendo following the merger of Microsoft and Activision Blizzard King.  Microsoft is committed to helping bring more games to more people – however they choose to play. @ATVI_AB" - text of Spencer post
Since the deal was announced in January, it has been the subject of regulatory scrutiny as it was feared that Microsoft would make the Call of Duty games - routinely the top sellers in the US NPD sales survey - exclusive to the Xbox console platform and PC. Sony in particular has been fighting the deal on these grounds as they currently have a marketing deal with Activision for Call of Duty games (including new console bundles) and want to maintain the game appearing on PlayStation without having to deal with an ostensible console competitor.
Call of Duty did appear in various forms on Nintendo platforms in the series's early years, but has not been present on a Nintendo system since the 2013 release of Call of Duty: Ghosts on Wii U.