A1GP was a failure for several reasons, none of which affect F3:
-It was centered around nationalism, which doesn't go very far in motorsport. Coming from a certain country doesn't make you good, and never has.
-Because it was a nations-competing series, the car's featured flags...which took away a key area of sponsorship. So there was little money behind the series.
-The cars were not particularly good.
-The drivers were lacking, partly because of the nationalistic thing, which meant drivers were being picked for their birthplace, and partly because it ended up with a lot of mediocre drivers anyway.