Going to marriage counselling shows that you are both prepared to work on the relationship. It helps to have a neutral third party to keep the peace if tempers get frayed. They will also ask questions which might give you a different perspective on the problem. And you may hear your spouse talking about things and realise that you had no idea he felt that way about them.
Couples counseling probably helps them by giving them a place to lay out everything before them with an outside person to call them out on their issues and help them to see what they need to work on and where to start. The counselor also provides ideas to help them get their own conversations going that may be new and/or challenging to really work through. She or he may also get them to try new adventures with each other in order to help rekindle their love for each other and really have fun and enjoy each other’s company again.