I can't tell from your post if the blinds called too. But you have something like 5-7 people seeing a flop with 3 to a straight and 2 to a flush, and to top it off an UTG player who wanted to bump it up to $200 preflop. UTG could easily have aces or kings here and is now scared, b/c that board is really scary in a big multiway pot. I wouldn't even be worried so much about UTG, you're probably beat from someone behind you, to a straight, two pair, set, someone with two overs and a flush draw. I don't think it's "weak" to fold here. With that board, an UTG who wanted to bet $200 preflop, and 3-5 people to act behind you, I think calling would be foolish.