People have been doing this for ages. Even the Abrahamic Monotheism proclaims THREE GODS: YHWH, The God whose Son is Jesus, and Allah.
Though they may not put it this way, for some, if one is going to worship God, the more the merrier.
One may compare it to this: If you enjoy art see more than one painting. If you enjoy novels, read more than one.
Music is one, but it is enjoyed in different modes: songs and serenades, symphonies and sonatas, chants and canticles, and more. Likewise, the Divine can be experienced in many ways.
For those who worship many gods, each is a visualizable representation or manifestation of the same single abstract Divine Principle.
Spurts of Thought 