There are lots of ways around doing a full SSO integration, though.
In the simplest form, the ISP could simply use a captive portal of some sort directing the user to authenticate first.
While captive portals can’t serve the correct certificate most browsers these days are smart enough to detect a captive portal redirect and give the user a smoother experience.
I definitely agree that these types of blocking are ineffective and generally do more harm than good, but if governments are going to push for this stuff, it would be good to have a solution that doesn’t harm people’s security and privacy.