What is the connection between detergent enzymes and sustainability?

I was looking at the shelf with "ecological" detergents in a store and noticed that most of them boasted of being enzyme-free.

I wondered why this is a preferable quality in a detergent, especially seeing that they are there to make the detergent better at washing. Since these were the ones branded for sustainability-minded customers, I assume it is supposed to have an impact in that direction. So, from a sustainability point of view, what are the pros and cons of using a detergent that has no enzymes?