I'm not sure Anderson is much better of a defender than Ilyasova/Morris, but he's exactly the high volume sharpshooter that would complement Drummond. And the reasoning is sound. If Anderson wants to team up with SVG again, there's no reason to give up assets now. This team isn't one Ryan Anderson away from contending this year. Better to look for other trades (maybe a SG that can actually shoot and stay healthy) that may fit with next year's roster.
Side note: Anthony Morrow, a perennial backup SG with a career 43% from three is all but out of the rotation in OKC. He's also signed for a pittance (3.3 million/year) through next season. OKC might dump him just to save money on their tax bill. Now, we can't take him on for nothing (we are over the cap), but we could certainly pay off a team like Philly with a 2nd rounder to foot the bill of say Steve Blake in order to make the numbers all work. OKC saves something like 10 million in luxury tax bills, we get Morrow, and Philly takes on Steve Blake for the price of one 2nd rounder.