There are four main reasons, and they are finances, time, the ability for your voice to be heard, and the emotional cost.

Mediation is much more cost effective, (even if you have both have lawyers, I the mediator can do a session and give both parties questions to ask your lawyers – which saves you time and money).

Time: the court system can take months or years to hear PARTS of your case, mediation can be done in months to a year to solve the ENTIRETY of your case. 

The opportunity for your voice to be heard. In court your voice will rarely be heard as you have hired a lawyer to speak for you. In mediation even though you have a lawyer, you will most likely be in mediation with the other person, and you will be speaking, instead of your lawyer and instead of a Judge making decisions for your life, you and the other person will come to consent on decisions for both of your lives. 

Lastly, the emotional cost. Mediation can be less stressful than court, and lessen the emotional cost that separation, divorce, and dealing with estates and estate sales can be.