Actually, Ganon is more often a transformation of Ganondorf himself instead of merely a form meant for all power. In A Link To The Past, Ganon's backstory is that he was originally Ganondorf, but became Ganon only when he gained access to the Sacred Realm (where the Triforce resided) and was turned into what became known as Ganon when he claimed the Triforce and took over the Sacred Realm, turning it into the Dark World. This presumably holds true for other 2D Zelda games, as well.
It's only in Ocarina of Time and Twilight Princess that Ganon is a summoned form of Ganondorf meant for pure power.
To add onto this, after Ganondof took over the Sacred Realm and transformed it into the Dark World, the corruptive power reflected the true nature within a person's heart and turned them into an appropriate form. Ganondorf Dragmire became a ferocious and demonic boar because of his lust for power and savage nature, while Link (briefly) became a pink bunny because - well, he's a nice guy, I guess?
I think the same principle applies in
Twilight Princess: Link, upon entering the Twilight Realm, is transformed into a wolf to reflect the courage and ferocity in his heart; Ganondorf becomes a boar, as he is wont to, but I don't think it's because of the Twilight Realm's power, but rather because of thematic reasons.
Ganondorf's spirit manifests the hatred of the Demon King Demise, and he's blessed with the Triforce of Power, so while his natural form is Ganondorf of the Gerudo, he can manifest the latent power within his soul in the form of Ganon.
It's not really intended specifically for power, as Dastardly says, it's moreso his true nature manifesting itself as a Hail Mary to defeat the heroes once and for all.