[saxonww]

The steel used to make the knives is not always stainless, so it can stain or rust. Even stainless is really just stain resistant.

Dishwasher detergent is caustic and corrosive to steel, so over time it can pit the metal and dull the finish. Handles will swell and become loose or deteriorate, either because of wood repeatedly being waterlogged and dried or just from the heat cycling. A loose handle can be unsanitary, unsightly, dangerous, or all three.

You'll often read that knives in the dishwasher will bang around and that will damage the edge. And that it's more likely you will hurt yourself pulling a knife out of the dishwasher vs. cleaning them properly.