He's on the market because no one really wants him that badly. Sure, teams with an open spot would take him for the min, but no one's carving out room in their rotation for him. Looking at rosters now, the only team I could see him getting consistent minutes on is Cleveland, and that's only because they traded away so many wings this summer. He certainly wouldn't (or shouldn't) get them in SA. At best, he'd be the fourth-best wing, and he'd be the sixth best perimeter player (seventh when Patty returns). And that's only if you think he's honestly better than Beli, which is definitely debatable.
I don't get it: What sense would it make to have a fourth two-guard over a third (healthy) PG or a front-court player? The Spurs already have Anderson to fill in spot perimeter minutes that result from injuries/rest. No need for Allen at all. And Ray wouldn't make the Spurs a better contender at all, since he wouldn't even be on the floor during the Finals. Seriously: Who would you replace in crunch time to get Allen minutes? The answer is no one, so there goes any value Allen could possibly have.