A big reason why it dies off after the first round is that most guys don't care once their team is eliminated. They find other things to do, either on HF or elsewhere. And during the summer, it's accentuated.
Some of our GMs are basically only all-time draft participants. They're rock-solid and reliable during the draft. They're fun to have around. But the only reason they're on HF is due to the draft. Once their team is finished, they're not around for a few months, until the next draft.
I think VanI's suggestion has some merit. 24 hours to discuss. 24 hours to vote. It's not like winning this thing really means anything in the grand scheme of things: it's an on-line fantasy draft with a bunch of guys I'll never meet, with no cash prize or trophy. No league fee. Once the teams are picked, and discussion of the rosters is finished, my interest dips considerably. And a significant portion of the discussion amounts to arguing in circles.
The reason I like the one-week round is that everybody knows when votes will be due. Start the threads on Sunday, continue to discuss through Tuesday, open voting on Wednesday and Thursday (discussion remains open during the voting days, although most valid points have already been made). Votes are tallied and released on Friday and Saturday. If write-ups will be part of the process, they will have to be done by Saturday night. It takes a little longer (five weeks), but guys know when things have to be finished, and they have two days to vote.
The way it is now, the playoffs drag way too long, the discussion period takes too long and winds up going around in circles, and guys don't know when they will need to vote.