Why are the fireplaces in European countries so clean?

Most fireplaces use natural gas or electricity and a small amount of alcohol, so the glass in front of the fireplace can't be opened. It's clean and there is no smoke. The mixed furniture and Zhandong carpet make this room not present a typical Nordic style, but the comfort and natural temperament created by the black and white gray color scheme, special fireplace and clean wall are in the same strain as the Nordic style.