Hmm. For me the difference, and it's not much of a difference, is that historical figures like composers and poets and writers tend to represent something larger and more abstract than themselves, and something more specific and (IMO) less self-deluding than "family history." They become avatars for things like... I dunno, for example
Haydn for me is sort of like the greek god of sunshine happiness. And if I were to honor an old ancestor, even if it were one who had a good life, it would be like honoring the greek god of please-let-me-stay-important-I-dont-want-to-die-can-I-earn-my-way-to-not-dying-by-living-well?.
I say this as someone who used to comb obsessively over family trees and want to honor ancestors from generations and generations ago. I'm talking about my own former feelings.