UK citizens also won't be able to appeal all the way up the EU courts: it stops at the UK supreme court.
And most importantly: now that the UK is out of the EU, it is a tiny, barely relevant factor in multinational corporate online practice. Any business that gets told by the UK to follow their GDPR can quite comfortably go "lol, no" and barely affect their bottom line, as opposed to having the entire EU block go "obey our GDPR or we won't let you do business in any of these 27 nations, a large portion of which make up a substantial cut of your global revenue".
The biggest players won't, of course, but smaller companies?