Novels have much more space than short stories, which gives you more leeway with the number of characters you can include. Even 'furniture' characters can be described and given speaking parts to develop background or atmosphere.
Surreal fiction is a sophisticated art form. Events happen divorced from conventional logic, as events in a dream may happen. But unlike dreams, everything in the story contributes to an overall coherent point, impression or emotion.
Overpopulated fiction can be so confusing that readers put the story down. Under-populated novels can seem claustrophobic or boring. You want the right number of characters for your particular work.