A couple of different ways to look at God. There is a God, but it is not quite what it thinks it is, or that there is no God that is permanent, omniscient, and the creator of the universe:
Now the question: why is union with God is a lesser goal? The Buddha states (Anguttara-Nikaya X 29):
'As far as the suns and moons extend their courses and the regions of the sky shine in splendour, there is a thousandfold world system. In each single one of these there are a thousand suns, moons, Meru Mountains, four times a thousand continents and oceans, a thousand heavens of all stages of the realm of sense pleasure, a thousand Brahma worlds. As far as a thousandfold world system reaches in other words, the universe], the Great God is the highest being. But even the Great God is subject to coming-to-be and ceasing-to-be.'
And in the 83rd discourse of the Middle Length Sayings:
"God truthfully answers [the questions of the Buddha] in succession: 'Good sir, those views I previously held are not mine; I see the radiance the world of God as passing; how could I say that I am permanent and eternal?'"
In other words God is still bound by karma and union with God is still to be within the realm of karma, which is inferior to the attainment of nirvana.
In Digha Nikaya 24 where the Buddha states:
"There are some ascetics and brahmins who declare as their doctrine that all things began with the creation by God, or Brahma."
And this singular god is characterized so:
"That Worshipful God, the Great God, the Omnipotent, the Omniscient, the Organizer, the Protection, the Creator, the Most Perfect Ruler, the Designer and Orderer, the Father of All That Have Been and Shall Be, He by Whom we were created, He is permanent, Constant, Eternal, Unchanging, and He will remain so for ever and ever."
which is a nice characterization of the brahmanical notion of the creator God one finds in the early Brahmanical and Ishvara literature, and it seems to fit for most every other creator God notion that has come down the pike.
The Buddha goes on in this discourse, using mythic language, to give a biting satirical re-telling of the creation myth of the Brhadaranyaka Upanishad making it quite clear that God is not quite what the absolute entity it imagines itself to be. It is not the creator, and we can see in this discourse by the Buddha and in other related ones that the idea of a single, absolute cause for the multiplicity of things, an infallible source of revealed knowledge that was different in kind from ordinary human knowledge, an unconditioned being that participates in any way in (even only as a witness to) the changes of human experience, and any kind of being that can interfere with the natural consequences of karma is rejected by the Buddha.
Elsewhere the Buddha states:
Anguttara Nikaya 3.61: "Again, monks, I [the Buddha] approached those ascetic and brahmins and said to them: 'Is it true, as they say, that you venerable ones teach and hold the view that whatever a person experiences...all that is caused by God's creation?' When they affirmed it, I said to them: 'If that is so, venerable sirs, then it is due to God's creation that people kill, steal ...[and otherwise act badly][/b]. But those who have recourse to God's creation as the decisive factor, will lack the impulse and the effort doing this or not doing that. Since for them, really and truly, no (motive) obtains that this or that ought to be done or not be done...."'[/b]
"If the pleasure and pain that beings feel are caused the creative act of a Supreme God [Issara-nimmana-hetu], then the Niganthas [Jains] surely must have been created by an evil Supreme God." MajjhimaNikaya II 222.
"The universe is without a refuge, without a Supreme God." MN II 68.
And then let us add these statement from the Pali Canon:
"He who eyes can see the sickening sight, why does not God set his creatures right? If his wide power no limits can restrain, why is his hand so rarely spread to bless? Why are his creatures all condemned to pain? Why does he not to all give happiness? Why do fraud, lies, and ignorance prevail? Why triumphs falsehood, - truth and justice fail? I count your God unjust in making a world in which to shelter wrong." J VI.208
"If God designs the life of the entire world -- the glory and the misery, the good and the evil acts, man is but an instrument of his will and God alone is responsible." J V.238.