God's Word tells us this. Proverbs 28:9 and Jeremiah 11:14, for just a couple of examples of how just because someone "prays" doesn't mean the Lord listens.
It’s nice that you believe this. Many others, do not.
I think most Christians will agree that God doesn't hear or respond to all prayers.
But it's really dangerous to set yourself up as the authority competent to decide which He hears and which He doesn't.