Because they wanted to tell us that it was their mutual decision and not to troll them. They are separating as couple but they can continue as good friends after divorce too, just like Hrithk Roshan& Sussane Khan( I feel that is nice). We need to stop think about any celebrity's decision at some point and just leave it as their personal. So, I'm stopping to think about their personal decision.
There are young people out there who have taken them as role models in areas like relationships. By doing this they have let them down.
How and why is anyone getting fooled here? Did someone invest in that relationship and lost all the efforts? The divorced celebrities are grownups and they are living their lives and handling life's ebbs and flows gracefully or in whatever best way they know. Well, it might come as a shock or disappointment to see seemingly perfect relationships falling apart. But, accusing them of fooling people is a bit out of line.
I guess people who are taking them as their role models forgetting that celebrities also just like humans. We should remember that what to follow and what to not follow from anyone's life or any culture.