The United Kingdom exists and some people are loyal to The Flag of the Union (commonly misnamed the Union Jack). England, Scotland, Wales and Northern Ireland are more historical titles than modern realities (although the situation is further complicated by the separate nations having their own sports teams and recent Parliamentary Acts granting some devolution). The creation of the Union in 1707 was a complicated political solution that is older than your country by some 69 years, so please excuse the British if they don't jump to your tune on this matter.
I don't understand what drives you to call for the disbanding of the UK (in a Chess.com sense), how does it's existence impact negatively on your life?
Live and let live.
Regarding chess.com members from different countries, why is there a United Kingdom?
It makes no sense to have this, if you already have a separate Scotland, England and Wales.
Disband the UK region and let individuals choose whether they are English, Scottish or Welsh.
(Besides I can guarantee that most of the constituents of the "United Kingdom" region will swell the ranks of England).