Nintendo's first and foremost objective is to make money for its shareholders, and shareholders hate declining quarterly statements.
Console development cycles take a long time nowadays and it's very hard to imagine Nintendo began this one betting the generation would last much longer than 6-7 years when their past four generations of home consoles were relatively short-lived. Most things about their next hardware must already be finalized or close to finalized.
So yeah, they don't *need* to, but they *will* release it this year, barring some unforeseen disaster.