I've actually used a mortar and pestle to prepare huge quantities of pepper for evenly coating a 17-pound prime rib, so I can answer that.

First, if you use a mortar and pestle, peppercorns will randomly fly out. This is not convenient.

Second, it will take you a long-ass time. This is also not convenient.

Third, you will have basically no control over evenness of grind/crush. And that evenness helps.

I know the $200 will make many folks blanche, but I'm telling you, that all melts away once you use this thing. :)