In this country, Matrilineal inheritance of titles and property are the norm. Magic in this world allows an individual to determine the sex of their child while it is still developing. There are a number of steps to this ritual. Gestation must be paused during the third month mark. Special herbs must then be ingested regularly at certain intervals. These herbs are specific to the sex that you want, either a boy or girl. Other medicinal herbs are taken to ease or even inhibit the strain of pregnancy (morning sickness, cramps, etc). After an exact amount of time, say one year from the beginning of the ritual, gestation can be restarted as normal. If steps are followed properly, the ritual is always guaranteed to work.
What incentives would there be for someone to have a boy in this scenario?