Wondering why some third party ports to Switch come out months after the game hits PS4/XB1? It all has to do with the dev cycle on those games. According to an interview with Nintendo's Reggie Fils-Aime, we should start seeing more third party games arriving day-and-date with PS4/XB1 versions by the time the year closes out.
“We’re talking today about a platform that is 16 months old. The development cycle today is multiple years. So I would argue that beginning at the end of this year, or next year, that gap will have closed. Because key developers have had the development systems, they’ll have been working to create content for our platform from the beginning. That’s what is going to close that time gap.”