Because they are praying in unbelief. They essentially don't believe that God Himself will answer their prayers as HE promised that He would. IOW, they don't take Him at His word.
It is all about FAITH. If God says it’s so, then it’s so. No matter WHAT. And without faith, it is impossible to please God. Funny, the eucharist is something that is taken purely by “faith” and catholics don’t seem to have a problem believing THAT is God-given. And yet.. prayer...I mean, really, God is changed from a wafer to His Body literally, and yet prayers are given to “saints” to offer to God?
Reading the minds of 1.2 billion people? How does one truly know the state of another’s soul? That is between the person and God. Even then, in His Eternal Wisdom, it is He Who knows the ultimate truth.