I assume because it is a relatively new city planned to replace Seoul as the capital city to reduce congestion. Its population would be mostly people from outside moving into the area, and elderly people tend to be more set in their ways and less willing to take risks like moving to a newly formed city.

1. Why does it say where T: Sized for references &T? A reference can definitely point to an unsized type, e.g. &str.

I think the point being made is that the layout shown only applies for Sized T. Layouts for &[T] and &dyn Trait are shown elsewhere on the sheet. &str is noted under &[T].

Edit: although, similar considerations would apply to other pointer types, but that isn’t noted on the sheet except for Box<[T]>