I can only assume a mechanic like attacks of opportunity or zones of control wasn't' implemented back in the beginning because of technical issues or some such. But the game really needs them. As it stands, bad guys are able to move in all kinds of ways with impunity, when really, without caution, they should be taking a great axe upside the buttocks. But don't think I just want it applied in favor of PCs. I want the bad guys to have the opportunity as well. It would make Tumble more useful, as per pnp, instead of the waste it is now. You would have to decide more to turn and run, exposing your backside, or withdraw backwards, more slowly.
Seriously, it's time. I'm thinking Update 19 maybe.