Because the film has been out of print physically in Region 1 (North America) for over a decade and is not available on any legal streaming service (Netflix, Hulu, Max, etc.), uploading the film constitutes "abandonware" or preservation.
For years, Godzilla vs. Mechagodzilla II was distributed in North America by Sony/TriStar. The English dub produced in the 1990s (featuring voice actors like the late Steve Bulen) is considered "cheesy" but nostalgic. When Sony’s physical media rights expired and Toho became increasingly protective over international digital licensing, the film disappeared. godzilla vs. mechagodzilla ii internet archive
It is copyright infringement. However, Toho often turns a blind eye to non-commercial archival uploads as long as they are not monetized. The uploaders rarely face legal action; instead, the files are simply deleted. Because the film has been out of print