Before 1917, British Royal Family had no surname, but only the name of the house , why has this changed?

King George V changed it because their current house that time was Germanic so they adopted that sounds British. Queen Victoria belonged to the House of Hanover and she was the last monarch of that house reigned in the UK. She married her cousin who belonged to the House of Saxe-Coburg and Gotha. Therefore their children belonged to the house of the husband. The first king who reigned in the house of Saxe-Coburg and Gotha in the UK was Victoria's eldest son, Edward VII. His son in turn was Saxe-Coburg himself but subsequently changed due to Wirld War I outcries. So, he became king as Saxe-Coburg and died as Windsor. Had he not changed the royal house, Elizabeth would be the last monarch in the house of Saxe-Coburg since she married the Greek Prince Philip whose house is Schleswig-Holstein-Sonderbyrg-Glucksburg… But there's a change again. Elizabeth II let it known that their children and their male-line grandchildren and so on shal bear the name of Mountbatten-Windsor. Mountbatten is the anglicized name of Battenberg from his mother's because "Battenberg" is German. I believe he did not take his father's name because it, too, sounds German but still he belongs to that house legally. So once Charles becomes king, he should belong to the House of Schleswig-Holstein-Sonderburg-Glucksburg legally and rightfully be the first monarch to belong to that house in the UK.