Except for "winner takes all" SnGs like heads-up and most spins, there is a bubble in SnGs, and its more important than in most MTTs. A simple way to look at it is, how much of the price pool is distributed, when the bubble burst. In most MTTs its around 30%. This basically mean, that after the bursting of the bubble each chip only has 70% of the value, it had at the beginning of the tournament, because there is only those 70% left to fight for.
In a traditional 9-man however the payouts are 50/30/20, and this mean, that 60% of the price pool is distributed, when the bubble burst, and after that each chip is only worth 40% of, what it was at the beginning of the tournament. So accumulating a large stack and "going for the win" has much less value in a 9-man SnG, than it does in an MTT, and on the other side surviving the bubble is similarly more important.
Another more intuitive way of looking at it is, that in the 9-man SnG winning the tournament only pays 2,5 times as much as min-cashing, and therefore a lot of your ROI is going to be determined by, how often you cash. In an MTT on the other hand, the winner might take home 20 or even 100 times as much as the min-cash, and therefore more of your ROI is going be determined by, how often you win or at least reach the top places.