File this under "Things That Were Obvious Before They Happened".
Before we get started, the most important element of contract negotiations is leverage. (It's the most important social element of life, but let's take this one step at a time.) What were Kurt Angle's options?
The WWE probably had some degree of interest in picking him up, but if any, it was very muted. The WWE is going through a youth revolution right now, and added to their roster, how much would Kurt Angle offer to them that they don't already have? There's probably more of an interest now then there was last week, after Edge got the Ricky Steamboat verdict- the W is running low on names with history with which to build their new guys. (HHH has a few runs left in him but I don't think he wants to use them, Undi looks to be down to about 1-2 matches a year, Orton and Cena will be around for a while. Chris Jericho will be back, CM Punk is big but not quite there yet.) I think he would have gotten hired back after a "you're sure you're straight now, right?" conversation, but he didn't offer the WWE something that they didn't have people for at the time.
He wasn't going to wrestle in restaurants (Hi, X-Pac! Hi, Sid Vicious!), and obviously, he chose not to retire. Unless he's been entirely foolish with his money (he wouldn't be the first), he's able to retire and live to that ripe old age of 48-49 that so many wrestlers pop off at.
That leaves TNA. He likely got a good deal, because if TNA tried to put the screws to him, I do think he had options within the WWE. TNA also needs Kurt Angle. One thing they are christingly low on is performers who can slide up and down the depth chart. Kurt Angle could work a believable program with Amazing Red one month, and be world champion the next month. (Or be stuck in a program for months that gets short term laughs and does nothing to position the company for the near or far term future.) He's valuable for the same reason Chris Jericho is; he can do it all, and make the people he's working with look great while he's doing it.
Now let's just hope TNA hires him a car service.... and finds that dastardly Twitter hacker.