That's their idea of "progressive" - being forced to pass through it all.
The worse part is, once you pass it, you'll never want to be back. That leaves a huge gap (just like in the "non-progressive" realms, where you shoot for ICC directly after hitting level 80, and miss all of these... OS?... Nax?... Ulduar?... EoE?...What?... raids).
Because once you've passed it, it's no longer progressive for you. It's just boring - forming a subpar group (noone else interested), then crawling through the raid with them. That's why people leave, not because of buffed content. Only the time for realm-first achievements was when this whole idea was attractive. And that was about no more than a few weeks. Sad to see it go.