Why does the block always need to hover around the 10 minute mark?Why not 5 minute or 15 minute etc?What is unique about the 10 minute mark that it must stay there?
That's the time that Satoshi chose when he created bitcoins.
It is fast enough that the currency is usable, but slow enough to reduce the orphan rate and give the blocks time to propagate to poorly connected nodes.
Once the time was chosen, any change to the time requires a hard fork. People aren't going to want to accept a hard fork without a VERY good reason, and changing the average time between blocks is not a very good reason.