giving blood is a lot like taking a plane trip.
You spend your whole time waiting, filling out forms, standing in line, getting screened, talking with the other passengers/donors and in the end, all you get is a cookie and a bit of juice.
It's also really easy to develop a false sense of intimacy with the other donors/passengers. You're stuck in this process both working towards the same goal. You have past trips/visits in common so there's something to talk about and you can compare and contrast your experience along the way.
And best of all, you'll probably never see these people again in your life.