I don’t see anyone disciplining Bishop Ackermann...
He has expressed an opinion - and demonstrated his poor understanding of Church doctrine.
Ackermann has, however, been very careful not to issue written instructions to his flock to disobey Church teaching, nor has he presided over illicit remarriages, nor has he authorized his clergy to do so, nor has he taken any other actions to "put his money where his mouth is."
Because, if he does, he knows he will be disciplined.
He knows the Hans Kung line, and he knows not to cross it.
Discipline in the Church is not arbitrary: it is canonical.