The answer is already for them. The tide of the feelings run high and it looks for a while as if revival might be on the way. But it fails to arrive and the zeal to prayer begins to flag. Soon the church is back to where it was before. God is not the hindrance.
Prayer is never a substitute for obedience.
To obey is better than sacrifice. Here is your principle tha has been violated. Prayer will become effective when we stop using it as a substitute. God will not accept praying instead of obeying. We only deceive ourselves when we try to make this substitution.