Like I said earlier, it's a keep busy fight, and since they're considering making welter again soon it makes sense to take on someone of limited threat at middle since they might be planning on Paul coming in the ring at low 150's.

If he were moving up permanently it'd make sense to test the waters with a Vera, but even as limited as Vera is Williams would have to bulk up 'properly' to match the guy in strength, which would severely damage his hopes of coming back down fast and safe (a la Roy Jones).