Because generally, the brahmacārī was going home at the age of twenty-four years, twenty-five years. So after marriage, he may get a child. So living there for twenty-five years, means the child is grown up. Then the husband and wife takes leave, not leaving for good, but vānaprastha, traveling in pilgrimages like Vṛndāvana, Prayāga. That was the system. And after two months, again he comes back and remains home for another two months. Again goes out. In this way, the whole process is how to give up attachment from this family life, from this world. And when he's trained up fully, he takes sannyāsa. That is our Vedic system.
So the attachment of this material world is very strong. That is stated in the Śrīmad-Bhāgavatam by Ṛṣabhadeva: Puṁsaḥ striyā mithunī-bhāvam etami (SB 5.5.8). This whole material world is an attachment of male and female. Puṁsaḥ striyā mithunī-bhāvam, sex impulse, attachment. Tayor mitho hṛdaya-granthim āhuḥ. And when they are married, when they are united, then it becomes a hard knot in the heart.