One reason might be that it's a style preferred by the creator. Yes, it could be a purely textual conversation between two people but, for example, the textual

One reason might be that it's a style preferred by the creator. Yes, it could be a purely textual conversation between two people but, for example, the textual expression of the second-to-last panel might simply be: Alice: ... Bob: ... Certainly there is a point that a person does not have to see value in anything other than the words but I don't get why it should be so perplexing for a person to see value in the illustrations. (I say perplexing because of the phrasing, "Why even bother ... ?".)