Any arc source is vastly more destructive with DC. That makes switching and circuit protection more difficult/expensive. AC helps you because the voltage cross

Any arc source is vastly more destructive with DC. That makes switching and circuit protection more difficult/expensive. AC helps you because the voltage crosses zero twice every cycle so normal voltages don't tend to be sufficient to sustain much of an arc in air. Every time you flip a switch you cause an arc, but the same DC voltage eats up the contacts more quickly. Even silly things like unplugging a running appliance does way more damage to the receptacle and the plug under a DC load.