If you play one character through-out the entire franchise, you can accumulate anywhere from 80-125 tackles, 20-30ish TFL's and very little sacks. I use Jerod Mayo of the Patriots and I get those stats on average and about 4-5 FF's. I never intercept with my main guy normally, but once in a while I will get a sack. One year I played the Lions and had 8 FF's as Ernie Sims.
Yes, sacks are hard to accumulate unless you're playing against a horrible QB such as Derek Anderson. Even if you don't get sacks, super sim a few plays and you'll get them.