The original French word means false, imitation or artificial. Faux marbe looks like marble. Faux bois looks like wood. Faux porphyry looks like stone. Faux marbe was used by ancient Greek potters.
People are after the look without the expense.
Sometimes, faux is used for fun. Of course, there are times when someone wants to appear to have the real thing and hopes and prays no one notices. George Washington used pine painted to look like mahogany at Mount Vernon. To a fledgling collector, this practice can be maddening.