During the medieval age it was normal to arrange marriages in order to secure political allegiances or peace treaties in order to achieve land and also to accomplish the continuity of bloodlines. This was done among the nobility but also with warriors and common people. The constant treat of warfare was one of the main reasons for such things.
The shinobies (like medieval warriors) can die any minute: in missions, exams, at war or even attacked at home. Many villages, clans and kekkei genkai have already been extinguished due to such things. Now war can be unleashed soon. Kids, bonds, deep alliances and peace are needed more than ever in naruverse, in order to avoid total annihilation.
Arranged marriage can occur in Naruverse for several means:
. to assure the survival of a linage and a kekkei genkai or a secret technique, or even to create a stronger linage.
. to secure a current alliance or to seal a new one
. to seal peace treaties, and create new bonds between villages due to the kids that will have relatives in two countries.