No animal including human works for praise reward, in the end we all have to get paid for what we do. More importantly, the individual getting paid decides if the payment offered is worth anything - for most dogs that means food or play. The use of food is the most reliable method of making a behavior salient to animal when teaching it and then to reinforce this behavior. With the use of food, you can make praise a secondary reinforcer. However as apes, we put far more value on physical contact than dogs ever will.