Thomas and Wiggins are not sprinters so they'd have chased Terpstra for nothing.
The group needed a sprinter with a teammate who still had the legs to chase down Terpstra. Degenkolb didn't have one, Sagan was spent.
Cancellara figured he would have a better chance contesting the sprint, he seems to have developed the ability to sprint well after 200 km. Vanmarche probably figured the same.
Really interesting tactical dilemma and OPQS' numbers game finally paid off.
I was happy to see Wiggins do so well. I hope he rides it again.