Here is my email client window. You can see notifications regarding article change.
If would have opened a NON-Wikipedia email, I would only see the list of emails. This list would contain emails with the same sender and same cropped subject. All the emails look the same. This is very inconvenient.
Another inconvenience is that the subject doesn't fit the screen even if I open the email.
I believe that regular users, not MediaWiki employees, have much fewer MediaWiki projects they receive emails from (maybe 1-3) than the articles they are subscribed to. It means that the article's name is more important to them. The project name is actually already specified in the sender name, no need to double it in the subject.
As a result, the email subject could be not
"Project-name-you-already-seen-in-the-sender-field article with name Article-Name has been changed"
but something like
"Article-name has been changed by UserName".
The context of this is readable from the sender.