Why is assignment to 'this' not allowed in java?

The error I get from the compiler is "The left hand side of an assignment must be a variable". My use case is deep copying, but is not really relevant.

In C++, one can assign to *this.

The question is not how to circumvent assignment to this. It's very simple, but rather what rationale is there behind the decision not to make this a variable.

Are the reasons technical or conceptual?

My guess so far - the possibility of rebuilding an Object in a random method is error-prone (conceptual), but technically possible.

Please restrain from variations of "because java specs say so". I would like to know the reason for the decision.