While downgrading video quality in order to reduce stress on European internet connections isn't a new thing, having a downgrade pre-launch for an entire streaming service is something new.
Chairman Kevin Mayer recently stated:
"In line with Disney's longstanding commitment to act responsibly, we are responding to the request of European Commissioner for Internal Market Thierry Breton to work together to ensure the smooth functioning of the broadband infrastructure. In anticipation of high consumer demand for Disney+, we are proactively instituting measures to lower our overall bandwidth utilisation by at least 25% in all of the markets launching Disney+ on March 24th. In the coming days, we will be monitoring Internet congestion and working closely with Internet service providers to further reduce bitrates as necessary to ensure they are not overwhelmed by consumer demand."
Disney+ hasn't launched in all European countries yet. The French Government asked Disney to delay the service in France until the 7th of April, and most other European countries will have to wait until June - at minimum.