When we use a typical half-bridge topology we are emulating a sinusoidal reference by the average value the PWM in a period T. Given a sufficiently large inductance the current has a significantly large fundamental compared to the switching component.
However we are still effectively applying a square wave which has a number of components superimposed to the fundamental frequency. Multi-level converters have the advantage of generating an output voltage which is closer in shape (hence lower spurious components) to thefundamental reference than a two-level converter. This comes at the cost of additional circuit complexity.