Often, the specific "expanded" IMAX aspect ratio is only available on certain streaming platforms (like Disney+) and is excluded from physical Blu-ray releases.
This allows for easier uploading to file-hosting services that have individual file size limits. It also acts as a safety net: if one segment is corrupted during download, you only need to re-fetch that 500MB or 1GB chunk rather than the entire 50GB movie.
The filename uses "leetspeak" (replacing letters with numbers) to bypass automated copyright filters.