I didn't spend enough time on the website to determine if the distance is because of course limitations (not wanting to lap Prospect Park twice, I'd imagine), or if it's a gimmick of some sort tied to the cause. Either way, a 6k race is definitely an anomaly.
Edited: um, duh, it's a gimmick. From the website:
Cool cause. I'm sad I can't do it, but I'm really busy right now (understatement) and my race calendar is pretty much as full as it can get. Plus, it takes me like an hour to get to Prospect Park from my apartment. But... I read that there will be "two Grammy-award winning pop acts" at the after-race expo, so maybe, maybe I could justify it, if it was M.I.A. or Santigold, or some other cool Brooklynite. But it's the Roots and John Legend. The Roots did record one of my favorite albums of all time, they named an earlier album (also good) after one of my favorite books of all time, and they're from Philly and are very trendy right now, what with Jimmy Fallon and all... (And I can't leave out this freaking cool song, and - although I think he's otherwise kind of annoying - I do like this song of John Legend's. WARNING: link will play song, and song is soft and cheesy and might embarrass you, depending on your environment.)
Three short races, three weeks in a row? That's silly. Also silly is that I'm thinking about doing this race, too. My dad was a fireman, and I'm a sucker for supporting police and firemen.
On I went, out of the wood, passing the man leading without knowing I was going to do so. Flip-flap, flip-flap, jog-trot, jog-trot, curnchslap-crunchslap, across the middle of a broad field again, rhythmically running in my greyhound effortless fashion, knowing I had won the race though it wasn't half over, won it if I wanted it, could go on for ten or fifteen or twenty miles if I had to and drop dead at the finish of it, which would be the same, in the end, as living an honest life like the governor wanted me to. -Alan Sillitoe, "Loneliness of the Long Distance Runner"