Why did early frankish kings covert to christianity?

Although raised a pagan (according to some historians, he would be the last of the pagan kings), Clovis realized that a conversion to Christianity would be extremely beneficial to him if he ever hoped to secure the loyalty of all of the Frankish people. According to Gregory of Tours, his conversion came, in part, due to his marriage to the Burgundian princess Clotilde (daughter of Chilperic); her family was Arian, but she was not. According to the historian Roger Collins, however, Gregory should not be completely trusted in his account. 

a countries leader should be motivated by the common good of the country.