Why? Because Arial Unicode MS is owned by The Monotype Corporation and licensed exclusively through Microsoft. Downloading it from a random website is software piracy. Furthermore, these "free font" websites are notorious for bundling malware, adware, or trojans into ZIP files. You may end up with a keylogger on your Windows 10 PC just to save a few dollars.
For those with older installation media, you can sometimes find it under "Office Shared Features" > "International Support" > "Universal Font" during a custom installation. Free Alternatives for Marathi Typing arial unicode ms marathi font free download for windows 10
If you have an older computer running Windows 7 or 8 with an older version of Office, you can copy the ARIALUNI.TTF file from its C:\Windows\Fonts folder to your Windows 10 machine. Furthermore, these "free font" websites are notorious for