well because it would be fun to trash and there will be no way to know who what and why, it has been proposed that SP and voting be hidden at least I've seen it, but that goes against the uncensoured transparent public blockchain that this started off as 

Anonymous flagging would result in an account assassination turf war that would leave only whales left using Steemit and since the bulk quantity of content is produced by dolphins and minnows the platform would grind to a halt.

It already kind of goes on a little bit in the form of delegation and powered up bot flagging although a determined study can usually expose the source of the bots.