Why is the spleen so much more likely to burst than the other organs?

Splenic rupture: The spleen is normally fist sized but it can swell to several times that size, unlike other organs which typically do not swell to this degree. The spleen acts as a filter, swelling is a normal response to certain disease states. The capsule or encasement of the spleen becomes very fragile in its swollen state, picture an over inflated water balloon. A sudden impact may cause rupture.

It's not: But it's fragile and trauma can make it break.