For variable name reusing.
and for making sure that local variables not be used accidentally in dozens lines of copy&paste codes.
and also easy for comment out lately.
well, thats why you use methods/classes
currently someone could tell “its duplicated code”(only 1 → -1 change).
adding method like "addDirectionalLight(Vector3f color, Vector3f direction) would make less code here and avoid “{”(well i know method have 2 of them anyway)
its not wrong in this situation tho, but im always serious about code duplications, so i let know 
(because i know in big projects dupplicated code make a lot of issues and increase work speed logarythmic a lot)
Anyway going further, you could use ECS(in JME it have Zay-ES) and even make light as SUN entity 
but lets stay with simple things.