No matter how good your draw may seem on 3rd it's still the early stages of a draw. With 7s and 8s out in other hands, this implies a lot of low cards in th pocket for these players. This means you may be drawing slim for low, and need to make the flush for high, so don't go and reraise with this hand on 3rd. It achieves the big pot to tie others on, but by catching a total blank on 4th, it has done the same to you. If there wasn't more than 1 or 2 low cards out on 3rd, and they didn't stay then raising is a better move, as low cards are much more likely to be live.