However, I must say that museums are really useful, to understand the history of the world, and that's why people keep going there even though they're sometimes dissatisfied.

dissatisfied 是由前缀 dis-（表示"不、否定"）和形容词 satisfied（满意的）组成的形容词。satisfied 来自动词 satisfy（使满意），所以 dissatisfied 字面意思是"不满意的"，指对某事物感到不满意或不满足的状态。