Considering Valve can only suggest deals that publishers need to agree to, not like ti's their fault entirely. Valve just can't say "Ok these games are going to be x% off and that's how it's gonna be!"
Valve doesn't suggest deals much at all any more. Before the winter sale, publishers submit two discounts. One for the entire sale, and another if they get chosen as a daily. Those rates are set by the publishers. But which games get put on dailies and
how many dailies is totally up to Valve. In the year where Valve has more than doubled the number of games on their store, they are having fewer dailies than ever. Which means
most games won't get as high of a discount as their publishers allowed for them.
Sure, if a daily is only 66% off instead of 75% we can complain some about the publisher's choices. But when that game sits the whole sale at 40% off and never gets a chance to be a daily at all, that's Valve's fault
entirely.