I think the culture of not cropping out the person who reblogged this chain (i.e. Julia Louis Dreyfus) is sort of like an informal citation system. It's analogous to if I said "oh man, let me tell you this joke that my friend Julia told me". Whoever made this screenshot likely only saw this thread because they were following Julia Louis Dreyfus

They reblogged the overall interaction but didn't add anything themselves. They reblogged it from gumdrop which is why that name is there.