I would argue that this repetition is not essential. It happens when you assign a constructor argument to an attribute directly without any modification. But there are case where it doesn't appear:

  - the attribute has a different name
  - an attribute is set whose value is a function of more than one argument
  - an attribute is set to a constant value independent of constructor arguments

In languages requiring attribute declarations the minimum number of occurrences is 2 (declaration and initialization in a constructor). When declarations aren't required then it's just initialization.

How often such circumstances occur is another issue. The form of initialization that you mentioned is probably the most common so languages can provide shortcuts in this case.