It's not that I don't understand how it works, it's that you don't seem to understand that isn't how it worked before the update. Before the update, there could be motorcycles, machine guns, silencers, baseball bats, or all sorts of other fun stuff on day 1 at the trader. Obviously you could not afford any of it on day 1, but it gave you something to get excited about. To put it another way, there was always something I wanted to buy at the trader.
Now there is literally nothing I want to buy at the trader. This is new. This is a change. This is a result of their tying trader stock closely to gamestage. That's the problem.
It's FUN to get something more powerful than you would otherwise have at a given point in the game. The overall affect of Update 21, an excellent update in most regards, is that there is no way to have fun, at least for players like me. You can't buy anything fun and you can't craft anything fun. All the fun is gated behind endless hours of slow small step progression. I don't want to dig for a couple days with a tier 1 stone shovel and then updated to a tier 2, 3, 4, 5, and then iron 1, 2, 3... I want to raid a bunch of houses, do a bunch of quests, buy a motorcycle and a good gun to take on something more challenging and rewarding.
They have changed the direction of the game. It is their prerogative to do so. I'm just giving them feedback about their change in direction. To me, and players like me, which I would imagine is the solid majority of players, the game is all about looting. You want to loot something big, something cool, something that makes you excited. Getting a mid tier iron shovel when you're rockin' a tier 1 stone shovel is kind of exciting, getting a tier 3 stone shovel is boring.
So far, and granted I'm only on day 16, but also, I'm already on day 16, my playthrough has been extremely mundane and boring. I've looted nothing exciting, the vendors don't have anything exciting, it's just a slow trudge up the tier list one small step at a time and there is no end in sight. If you call yourself The Fun Pimps, then fun should be a primary focus in your game. Oh! Look! I just looted a tier 2 iron shovel! It's 2 points better than my tier 5 stone shovel, but alas, since it can't hold as many mods it's actually not as good. Fun.