Likely due to sweaty palms. It could be due to whatever a guitar neck is finished with but I doubt that would be likely on a Martin. The only sure solution is to give the guitar a, so called, "speed neck"; i.e simply achieved by scraping the finish back to the wood, but whether you'd be prepared to do that on a new guitar is for you to decide.

It isn't my idea of the ideal guitar and someone had done that to a Santa Cruz guitar I bought a decade or so ago - I had the neck re-finished - but I'd start by drying your hands, making sure the neck is clean and trying not to hang on so tightly as you move up and down the fretboard.