The grill function requires the heating elements to be exposed. For this reason, the heating elements of the mini oven (which is designed for grill operation with a grill spit) are not built-in, but are exposed.
Due to their design, covered heating elements make little sense in mini ovens, as this would lead to a further reduction in the size of the baking chamber. To utilise heating power and space effectively, small ovens (without microwave function) are therefore generally equipped with exposed heating elements.