I'm definitely far from an expert, but what I think it boils down to is two things: S&C and what the scheme is trying to accomplish.But, I see a difference in the zone blocking mentality that you mention where you're redirecting guys.....and expecting them to be pushed two yards back.
S&C is pretty straight forward - I think the playing field has really leveled itself out in the last 15-20 years making physical domination of another opponent more challenging. You can still get S&C wrong (oh hi Mike Riley) but there are more tools and knowledge available to get it right. As for scheme, I just think the spread doesn't really lend itself to that mentality of wanting/needing to knock guys down. The speed, the deception, the style. I think coaches place value elsewhere and need the players to execute a bit differently in order to have success.