HTML is declarative, but it's also a string. It is faster to manipulate the DOM to make the changes you want than to generate an HTML string and ask the browser

HTML is declarative, but it's also a string. It is faster to manipulate the DOM to make the changes you want than to generate an HTML string and ask the browser to parse it. A virtual DOM allows you to use declarative _code_ instead of a string to get the same benefits as declarative HTML, but avoids the overhead of HTML by manipulating the DOM directly under the hood.