You can't view blitzing a player in isolation and assume it will result in more sacks. First of all, this is a game and only an approximation of real life. But even in real life, as with GD, there is a trade-off. Blitzing gives you one extra person to apply pressure, but if the pressure is absorbed, your chances at a coverage sack are diminished by having fewer pass defenders. It is not necessarily the case that blitzing increases your chances of a sack. But that misses an important point that I want to make: if you want to increase your pressure and avoid making it blatantly obvious to your opponent in pbp data, blitzing is not the way to go. One caveat is if you want to blitz from the secondary, since you can't disguise that.