Because his decision was based upon the environment rather than the message.
In all 3 situations the Adversary has fallen in Scripture, it has been from an situation of perfect environment.
Environment is not the criterion for sanctification, although associating with evil may have adverse consequences.
Second, as the Scripture says, the whole world, all of creation, proclaims the glory of God. He made us sensitive to beauty in part so we would see His glory around us. There is nothing wrong with responding to the beauty of the created world, even if the beauty one is responding to is religious architecture intended to honor Him.
He chooses different means to speak to each of us. One person may hear a Bach fugue, another may contemplate the stars, another may (like me) study the miraculous workings of the cell, and in wonderment say, "This beauty could not exist without being ordained by a Creator," and start down the path toward Him. Just because the awe-inspiring beauty of a cathedral doesn't move you doesn't mean that this is not a valid way for people to hear God's call.
I find in general that it is neither wise nor charitable to presume that we know what is going on in the relationship between another person and the Lord, or to think that we know more about Him than someone else (unless of course that someone else is leading a life of wickedness).