Inexperienced designers (e.g. a large percentage web developers) like flat design because it's easy. Switching from skeuomorphic (with nice-looking buttons, etc

Inexperienced designers (e.g. a large percentage web developers) like flat design because it's easy. Switching from skeuomorphic (with nice-looking buttons, etc.) to flat (with simple boxes) lowers the threshold for just about anyone who knows basic HTML/CSS to make a website.