Because there aren't enough British dreamboats at this school.
Hey everyone! Courtney here to introduce you all to Brian Braddock, aka Captain Britain.

After the Weapon X incident, Brian decided that it was time for Betsy to come home where it's safe. Since she refused to do, so he decided the only way to keep her safe is to enroll at the Xavier institute.

Although his only reason for being at the mansion is to watch out for Betsy and a be an overbearing brother (a very, very overbearing brother), he'll be using this time as an opportunity to reinvent himself. Pre-Captain Britain Brian was a studious loner. He's now trying to be the outgoing, confident socialite he thinks Captain Britain should be both in and out of the costume. When he first arrives at the mansion, he'll have alpha male syndrome, but he'll mellow out a bit when (or if) he realizes he doesn't have to prove himself.

No one but he and his sister know that Brian Braddock is really nationally acclaimed Captain Britain and he wants to keep it this way. While he's at the mansion he'll be living a double life and flying off to randomly save Britain from disaster, because it's his duty. I doubt in a school filled with mind reading telepaths and people with enough intelligence to notice Brian disappears a lot this will stay a secret forever.

That's all the important stuff about him. Check his profile if you want more information.