I wonder if its because the bushings are actually also just so freshly completed production and we are buying them like day 0, when probably almost any other time we have bought trucks in our life they have likely been sitting around for quite a long time, possibly even years? Would line up with why those brand new Purple Inverted Kingpin bushings took awhile to firm up still as well. They may just need a little longer to cure in general.
I've had my trucks since the first shops got them and the bushings didn't firm up more substantially than anything else I have recently had. They firmed up some over the course of an hour, but after that it was not substantial and they never dramatically changed. I've ridden them in 60-105F.
While old vs new urethane might rebound differently if it's very new or very old, bushings don't age that fast that we would experience such massive changes as @mbrimsob is hypothesizing. That would then mean that trucks that sit on a shop shelf for a few months would have super crusty feeling bushings and we all know from years and years of experience that things don't change that fast.
My guess is that since the pivot cups are also urethane you're seeing both those and the bushings breaking in.
I think it is more like years, eg these other older 2021 or so trucks, back when they used to still put the dates on the product stamp are significantly firmer than the newer inverted options, or the V8 blue bushings.
Any which way, it is not a big deal, but both of those feel like they work well for me now, but the standard bushings are a touch too firm for the most part, especially the older ones from earlier production runs, eg Thunder teams with yellow or dark green coloured bushings.
I also wonder if some places would go through product way faster too, so you guys there in USA who are already out of other things like 93 duro wheel, whereas we here in AU will most likely still have the current stock for a few years, going by stock levels, which is not a bad thing to me - means we have more options anyway.
Really too, this is all just thoughts, not facts, regarding bushing hardness, new vs old bushings and all that. Breaking out some new old stock of the white boxes of Indy low bushings, which are definitely ten plus years old now, they feel very firm at first, go super soft for a while and then firm up again after a couple of sessions, but I also think these bushings are a different urethane and perform very differently to the DLX bushings.
Also I just noticed one of my bottom purple bushings from the inverted Thunders has cracked now too, on the back toe side, which is funny as I never really have busted my DLX bushings, but have heard most other people talking about how they break and come apart. They still work fine, but it is just an interesting thing to note.