In the NBA, coach Phil Jackson has won six league title with the Bulls by using the 3-4 defense. In the NFL, many teams also want to make use of this system, but not every one of them can do it because the 3-4 defense is not very easy to grab and it requires the team to have certain abilities.
First of all the team must have players of high football IQ. No matter how well the defensive coordinator masters the scheme, if the players do not understand, it will just make them robots.
Then the scheme requires a hybrid who is athletic enough to have limited coverage skills and physical enough to dominate an offensive tackle, and sidekick who has coverage skills but also can dominate a running back and occasionally beat an offensive tackle.
A 3-4 defense must have a nose guard who commands a double team on run plays. He has to be the master between the guards. It also requires two defensive ends who can control the line of scrimmage and have the ability to beat one-on-one matchups on pass plays but must be dominant in stopping the run. Only a few players wearing steelers jerseys can do this.
So for the teams who want to use the 3-4 defense, they need to consider more carefully and weigh the players quality enough.