The idea is to make it public, humiliating and/or gruesome, so that it sends a message to the rest of them; a reminder of who they serve and why they are there in the first place. We are not supposed to be their slaves, nor are we supposed to kiss their feet and bend our knees to them. Many of us will only bend our knee to one entity, and that is by choice, not by force or coercion.
I think very few of us take satisfaction in the physical act of it, but with every action they take against us, the more justification we will have for a violent response.