How to avoid unchecked casts in a Java Generics extended Comparable interface?

Why is the unsafe cast (T) needed in this generic interface? If T is comparable to itself, i.e. implements ExtendedComparable<super of T> which means also ExtendedComparable<T>, then why does type erasure require ExtendedComparable<T> to be cast to T?

/* @param <T> T must be comparable to itself or any of its superclass
 * (comparables are consumers, thus acc. to the PECS principle 
 * = producer-extends,consumer-super we use the bounded wildcard type "super")
 */   
public interface ExtendedComparable<T extends ExtendedComparable<? super T>> {
    Comparator<? super T> getComparator();
    default boolean greaterThen(T toCompare) {
        return getComparator().compare((T) this, toCompare) > 0;
    }
}