It changes because the reference panel is constantly growing.
People read the info wrong, it's not as simple as saying someone is 80% English and 20% Eastern European or whatever.
You have to remember it's only an estimate, the larger the reference panel the more precise their estimates become.
And to those who claim they are a pure blood or whatever bollocks.
We inherit 50% of our DNA from our mother and 50% of our DNA from our father, which means that there's 50% of each parents DNA that we don't get. So we all could have a few skeletons in our closet and be non the wi