I didnt't have time to read all the responses, so somebody may have already said what I'm going to say.
It's called tournament strategy. It's not just a bubble tactic. The thinking is that we all want to advance deeper in the tourney (closer to the money, final table, victory). With each player that gets eliminated, every player left gets closer to victory, including you. Therefore, it is generally understood between more experienced players, that when a player is all in, and there is more than one caller with chips behind, that you do not bluff at a dry side pot. When you do, you risk running the best hand out of the pot and thus saving the all in player from elimination, and keeping every player, including yourself, from being that much closer to victory. Not to mention having one more player with the potential to take your chips left in the tourney. As long as there is no side pot, I usually continue to check the pot down even if I hit, but stay on stand by to shove all-in if the other player bets at it. Most experienced players will continue to check as well, the unspoken agreement being that the immediate priority is knocking the all-in player out. For instance, my Ace high might be ahead on the flop, but you hit a pair of 10s on the turn. An Ace hits on the river. The all-in player might be holding Js. So by betting the 10s on the turn, you would have pushed me out of a pot that you wouldn't have won anyway, allowing the all-in player to double up, instead of being knocked out.
I actually saw a perfect example of this the other night. With about twenty or so players left in an MTT that played 12 places, a player limped into the pot from early position. The short stack shoved all-in for about 8x (just under 5k). I called with A-Q suited. Another player called behind me. The early limper folded. The flop ccomes something like 2-7-10 rainbow. I checked pretty much automatically. The player behind me bets halft the pot. My thought is that everybody knows you don't bluff at a dry side pot with a player at risk, you check it down. So he must have a worthwile hand. So I fold. It turned out that he was holding K-J and fired out with air. The short stack was holding A-10 and made a pair of 10s. The turn is a blank. The river is a Q. So by bluffing at a dry side pot, that he wouldn't have won anyway, he allowed the short stack to survive and triple up. The funniest part (not at the time) is that about 10 minutes later I ended up all-in in a 3-way pot with the same two players. This time the player that had previously been at risk had us both outchipped, having won a couple of pots in the interim. He ended up flopping a set and knocking us both out. So this guy ended up getting knocked out by the person who's tournament life he saved by bluffing at that dry side pot.