Defenses have gotten way more athletic and O-lines havent kept up. Defensive ends are probably faster than ever and LBs are more athletic than they used to be as well. But for the most part O-lines haven't evolved much athletically, and in some ways have regressed. QB's have less time in the pocket, some have no time or pocket at all as soon as the ball is snapped, and RBs have fewer lanes/holes than before.
I think this is partly why the rules have been skewed in favor to the offensive side of the ball more and more.
If you look at what the Cowboys have built the past 5-6 years with their O-line, you'll see what the difference is. That line is a huge factor in the success of both Prescott and Zeke Elliot, and DeMarco Murray before that. Patriots do a great job of keeping their O-line on point as well.
It's not rocket science but it does take a while to build the pieces, and often teams don't want to make that commitment by spending draft picks in consecutive years O-linemen.
I think this is partly why the rules have been skewed in favor to the offensive side of the ball more and more.
If you look at what the Cowboys have built the past 5-6 years with their O-line, you'll see what the difference is. That line is a huge factor in the success of both Prescott and Zeke Elliot, and DeMarco Murray before that. Patriots do a great job of keeping their O-line on point as well.
It's not rocket science but it does take a while to build the pieces, and often teams don't want to make that commitment by spending draft picks in consecutive years O-linemen.