Personally I don’t think that sucks or is even wrong. Case-independent text processing is more cumbersome. ‘U’ and ‘u’ are two different symbols. And you have to make such rules for every language a part of your processing logic.
If people can take case-dependence for passwords (or official letters and their school papers), then it’s also fine for email addresses.
The actual problem is cultural, coming from DOS and Windows where many things are case-independent. It’s an acquired taste.