It’s legacy, white spaces weren’t allowed as characters on most FTP software, which is how the warez scene shares it’s releases. It used to be underscores, but dots are closer to a white space regarding separation (space wise), so most release groups use dots nowadays.
Generally, a white space as a character in filenames and directories is “frowned upon” in many operating systems, Windows included (somewhat). It makes writing scripts and software more comlicated because it’s used as as a separator for giving command line/terminal options to commands and binaries (programs).