Conspiracy theorists: GO!
I don't think it's very much a conspiracy, but let's see what has happened in the last year:
1) for months, years, whatever measure you like, woot has lost certain demographics shirt-side, even as they gained more viewers. There are people who were very active who rarely come around any more. This has been true for years. Think of any artist you see rarely-if-ever these days. Think of community members who no longer comment. People who are involved in one manner are more likely to be involved in other manners, such as voting.
There are plenty of reasons WHY they left, but let's simply look at the fact of them leaving.
2) Woot is classically for cheapos. Despite $18 being about market-price for a tee for years, people would complain about the $10-$15 price point, and complain more about other sites which dared offer their tees for $12 on the first day/week/month. So when woot upped their price, it is completely likely that there were some buyers who were lost, and others who began buying less frequently.
3) Woot's price hike was predicated on the cost of keeping AA blanks. Imagine the surprise when months later, the blanks changed to a well-known lower quality brand, but the price remained higher. The profit margin increased around $4 per tee, and the consumer got a noticeably worse product. This, as we still see today, had a huge impact on many users. For every person sticking around and saying "man, I wish this was on AA, but I can't buy an Anvil," how many people simply stopped checking? Because months later, there are still new people popping in and saying "guys, my last shirt was awful, I can't keep checking here if that's the quality I'm getting." This is a huge blow, since the one thing I could never fault woot on was an ever improving quality of product, even if the graphics on the product were exponentially worse.
4) The new derby format is a godsend to people who have been crunching numbers and analyzing the site and voting every week just to see the same trash win. Except most of those people have left already (see 1) or, being that they have higher standards for design, would likely have high blank standards as well (see 3). Basically, the change comes from a strong, reasonable mindset, but is enacted at a site that has driven away huge swatches of people with reasonable mindsets. With a majority of woot being of the "POPULAR IS QUALITY" mindset, this is seen as throwing away a vote to many, or else a betrayal of the democratic process. Ergo fewer votes.
I don't think any of this is conspiracy, but facts of what woot has done, how it likely panned out for some users, and compiled together, it's not unreasonable to see a trend that could lead to a downward voting trend. We're in a position where we have positive change coming in a too-little-too-late package, where the people who would praise it have long since been fed up with waiting for a positive change, following up a succession of negative change coming too-much-too-soon, with the one-two punch of higher price and lower quality.