Demand high, supply low
Nintendo has been pretty open about the Switch stock situation in recent months, as there are supply chain issues for a lot companies working in tech. The elements needed to build these platforms are in high demand and low supply, so manufacturing has slowed down for everyone. Not surprisingly, this is going to impact sales of numerous devices, Switch included.
Nikkei has stated the Nintendo expects to sell 10% few Switch units in this fiscal year as compared to last, which amounts to roughly 20 million units in total. The major issue stems from a semiconductor shortage, as well as disruptions to logistics networks .