Why the devatas, though not God, are called ishvara

Krsna Himself,    endowed with  sixty four transcendental qualities, is the perfect embodiment of  continuous rasa.16  Of these  fifty qualities are present in small  amount in  the  jivas.   These  fifty  qualities and  an  additional five  qualities are  present in  Siva, Brahma,  Ganesa,  Surya  and  other  devatas.  For that  reason,  though they  are  not  God, they  are  also  called  isvara  or Lord.

Chaitanya Shikshamrita, Bhaktivinoda Thakura