Obviously giving a discount on customs is less pressing for them than discounting inventory to clear it out, probably it's also a slightly worse deal for them money-wise too (less profit).
My guess is... (all of the following is pure speculation!)
Previously they were handing out those discount codes on cons (which are/can only be visited by a tiny tiny share of BD customers) in an attempt to keep relative control over the sales volume. Because they only handed out the code to a handful of people, they could allow for a longer time window in turn - or so they thought, as we began sharing the discount codes on the forums.
This however likely still didn't have a too big impact, because they just kept going with those generic, multi-use codes - they could easily have started handing out only-valid-for-one-order individualized codes if it had been a problem.
But now with their new website, there's no longer any way to enter discount codes, and the temporary solution to have customer support refund the discount after ordering was way too labor-intensive to be viable, and now we just get timed, site-wide discounts that are offered to any random visitor. There is no way to miss the discount if you are ordering in that time frame, because it is force-applied. So with that, now they have no more control over the size of the discount audience in any way at all, and to still keep some control over the discounted sales volume the only instrument they have left is shortening the discount time frame.
Maybe they had already decided for a "until end of week" sale for this event because of marketing reasons, but didn't want to discount customs too because of the too-long time frame?
Here's hoping they do a one- or two-day New Year's sale with discounts on customs...
Cosmic Nebula & Infinity Star
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19 pegs / 6 holes / stash of merch & misc