If God is the uncaused cause, as neo-Thomists and others assert, then his existence has no reason. His existence is simply a brute fact.
And if God's existence has no basis in reason, then there is also no reason to assert he is the solitary uncaused cause. He may very well be one of many uncaused causes.
And if God's existence has no basis in reason, then there is also no reason to assert he is the solitary uncaused cause. He may very well be one of many uncaused causes.