Even the juggernaut Deutsche Bahn (they handle public transport in almost every municipality) couldn’t break through these structures (eg the city of Munich just couldn’t be pressured to comply with their ticketing schemes).
In the end mandating it by the federal government was the only way. Although I’m curious who’s really benefiting from it: yes we solved the annoyances for the E-Mail caste, but the service quality itself will surely deteriorate by this measure.