Especially now that he had his foot in the door and an audience with the Areopagus, he wasn't going to say, "Let's talk about this. I'm interested in learning more about your approach to the spiritual disciplines and your ideas about ethics. And tell me what you guys think about the God of Abraham, and maybe we can learn from one another."
Instead, he homes in on the very heart of what he wants them to know. He is preaching here, not inviting a conversation. Here's the start of his sermon: "God, who made the world and everything in it, since He is Lord of heaven and earth, does not dwell in temples made with hands. Nor is He worshiped with men's hands, as though He needed anything, since He gives to all life, breath, and all things. And He has made from one blood every nation of men to dwell on all the face of the earth, and has determined their preappointed times and the boundaries of their dwellings, so that they should seek the Lord, in the hope that they might grope for Him and find Him, though He is not far from each one of us" (vv. 24-27).
Notice: this is a simple declaration of truth, not an offer to exchange ideas. He starts with the basic principles of theology proper. He declares that God is creator ("God . . . made the world and everything in it"). That's the essential starting place of all biblical truth. He affirms the authority of God ("He is Lord of heaven and earth"). He affirms the spirituality of God to these materialistic philosophers ("[He] does not dwell in temples made with hands"). And he affirms the sufficiency of God, His sovereignty, His transcendence, His imminence, and His power as the giver and sustainer of all life. It's a remarkable course in theology proper in a very brief economy of words. And all of it was flatly contradictory to what these philosophers believed.
But there's no give-and-take exchange of opinions. Paul does not act deferential in the presence of these great minds. He does not assume a false humility and pretend he's just a truth seeker on his own spiritual journey looking for companions along the way. He declares the truth of God to them with authority and conviction. He does not use the conversational style and subdued demeanor most people today think we need to use so that we're not thought arrogant.