In the first sentence, the meaning that I gather is that the average amount of time advertisements last. So you can see that the matter is to put forward a general fact and hence that would require a sentence to be in present tense. Hence long and NOT lasting. In Chinese philosophy, to be sure, the last is the lasting.

In the second sentence the subject is what the graph shows and there is no helping verb present in the sentence (in this case is ) which compels you to correct the verb following to follow since simple grammar does not allow us to use ing -words in the absence of a helping verb