Nike is a textile and foam company, so snowboard boots are a relatively easy jump for them to make. Ski boots involve highly intricate aluminum molds (molds alone can total 700k€), injection machines (each injection machine is about 500K€), plastic sourcing, and metal sourcing, let alone the many years of experience it usually takes to get good at it. Even if you include Nike Golf, Nike has very limited experience here but for sure the monetary funds to invest if they really wanted to enter the project. However, being primarily a "softgoods" company, what they don't have is the patience to wait the numerous years before they start making a profit off injection molded hardgoods. They want their ROI now, not in 4 years.
Remember Quicksilver's acquisition of the Rossignol Group? Hell, that was only an acquisition, and Quicksilver realized they couldn't make money fast enough off of an already existing and established hardgoods company, let alone try to start one up from scratch. I am fairly certain Nike and other softgoods companies know this story and as such as rather hesitant to enter into the world of winter sports hardgoods. Patience is not Nike's strong suit.