If I find an awesome list that someone else has shared, I may want to use that list as a basis for my own without having to manually recreate it (currently it's a bit cumbersome to create long lists). So it would save time. Also, if I could copy/import one of your lists, let's say, that would be a way for me to endorse that list by having it on my profile too and this, in turn, would increase the discoverability of all the writers that appeared on your list. Moreover, many users may be too lazy to create a list of their own, but would import a list they like if it was just a simple click. Again, this would help the writers appearing on lists to become more discoverable.