Since 2017, the company has only shipped titles like Super Mario Maker 2 and Super Mario 3D World + Bowser's Fury, which are linked to older games. Nintendo has yet to announce a direct follow-up to Super Mario Odyssey.
That point is disputed on both legal grounds and the benefit to the game industry. According to some legal theories, it's believed that failure to enforce copyrights and trademarks in one circumstance can allow more serious breaches later on. This is probably less out of maliciousness than a desire to set precedent.
Nintendo is infamously protective of its intellectual property, including fan projects that aren't designed to make money.
The game is currently available to download from Google Drive, but how long it will remain online remains to be seen.