Well there may be three things wrong:
You no longer have enough card points to get a new card.
You don't have the prerequisite card (for example in order to get the 4 vil card, you first need to have the 3 vil card).
You haven't got the sufficient HC level and you're just not paying enough attention.
"I found no one ripe for many of my thoughts; the case of 'Zarathustra' proves that one can speak with the
utmost clearness, and yet not be heard by any one." - Friedrich Wilhelm Nietzsche
"The fearless are merely fearless. People who act in spite of their fear are truly brave."
Oprichniks are the best units in AoE3. Why? It's elementary, they're Horse-riding Russian Pirates, nothing beats Horse-riding Russian Pirates.