All has to do with that strung out southern wave.
We were concerned about the northern wave early on, and in the end it's the southern wave preventing a more organized system.
0z NAM continuing the trend of a northern wave which dives in more. Looks like the southern wave ejecting out a bit strung out keeps this run from having a big dog. .
The trend on 6z guidance, and now continued on 12z guidance, is for the northern stream to be further west and dig more...which in turn allows for more phasing, and a better/further north storm system.