^I'm sure photo collage, like any other artistic medium, requires talent, practice, and a good eye to do well. We've all seen bad photoshop jobs as well as near-flawless ones.
Trust me, it's not as easy as it sounds. When I was in High School I took a Media Productions class where we used Photoshop extensively, and we'd spend entire classes working on one photo. If you have multiple sources, with different lighting, color saturation, ect. you can spend hours trying to blend things seamlessly, and that's only working with preexisting sources, if you have to create anything for it can take a lot longer. Hell, there were times in the class where I'd be blending things pixel by pixel trying to make them seamless, and that can take forever