Because, again, the Kshatriya wife, is not equal in point of birth to the Brahmani wife, hence the son of the Brahmani wife takes, one after another, all the best things, O Yudhishthira, among his father's property.
भूयो भूयोऽपि संहार्यः पितृवित्ताद् युधिष्ठिर। यथा न सदृशी जातु ब्राह्मण्याः क्षत्रिया भवेत्॥