This is probably my last response. It is to Chris:
(1) I appreciate the considerations in favour of unificatory explanations, but when I consider certain enduring artworks and certain other enduring artworks, non-identical explanations for their endurance occur to me and these explanations seem very plausible. I am not inclined to attach that much value to being unificatory, in such conditions. But you think there is a big price to preferring pluralistic ones, which I address below.

(2) Regarding the last sentence of your response, your thought, as I understand you, is this: either there can be a good unificatory explanation for the endurance of artworks or it is a metaphysical error to think that different artworks belong to a common type 'art'. I will grant that they belong to a common type. But why does that requires thinking that the explanation must be unificatory?

My knowledge in this area is very limited, but perhaps your argument is as follows: (i) the reason for us saying that artworks belong to the common type 'art' is because we think that all important properties that manifest themselves in different artforms admit of unificatory explanations; (ii) endurance is an important property that manifests itself in different artforms - there are poems, musical works, paintings, etc. that live on; so if we think that there is no unificatory explanation of endurance, we have no reason to say that artworks belong to a common type 'art'. It is an interesting argument. But (i) seems very controversial. I suspect that if one looked through theories of what is art, most of them do not require anything as strong as (i) or even a moderated version that still includes endurance in the list of properties requiring a unificatory explanation.