In our forum, besides the SPAM and self-promotion reasons for using shortened URLs, there are two legitimate reasons eg.
“I am working on a client’s site ______ and I can’t get the CSS right, please help”
Where the dev wants the client to not find out they were asking for help.
“I posted an example page on my website here ______”
Where the poster doesn’t want Not Founds to appear in their logs after the temporary page has been removed and would prefer to not need to constantly update their htaccess file.
So replacing them automatically all the time in our use case would not be a good thing.