Cat food has more meat protein = its yummy!

here is a link on why this happens and more importantly.. how to fix it http://www.helium.com/items/1577212-how-to-stop-a-dog-from-eating-cat-poop

They are hungry.

Not sure why they eat it, but I can offer a working solution to the problem:

After years of dealing with this, the best solution for us was to get an automatic cat box (a standard littermaid automatic catbox from Petsmart will work). We then had to take the ramp off the catbox (easy to take off, snaps in), and put the entrance end of the catbox up against the wall. That way the flap lifts up to allow the faeces and urine in, but the flap will fall back down when it is done scooping the cat litter. We had problems for a year of the flap falling open and the dog eating right out of the plastic tub the waste goes into, and the wall method fixed that. Now the dog can't keep the flap open to get the waste out of. It's a super simple and brilliant solution (partially by me, and partially by my wife).

This also helps with cats that don't want to use the catbox unless it is immaculate. They are often fascinated with the automatic catboxes, and very rarely scared of it. You might help them adjust by not turning it on for a few days, so they get used to the catbox without the noise.

The automatic catboxes have timers on them you can set for when you normally sleep, so it doesn't go off and wake you up. It is COMPLETELY worth the $100 you will spend for the automatic catbox, and the only thing that works and is easy to maintain.