https://www.techradar.com/news/praising-the-sun-dark-souls-on-switch-delayed-until-summer

It turns out that Dark Souls isn’t just notoriously difficult to play – it’s proving difficult to port as well. 

Dark Souls Remastered was originally slated to release on the Nintendo Switch on May 25, but Bandai Namco has announced that it won’t be launched on the Switch until an unspecified date in "summer of 2018" (so July-August).