Sure, unneeded things can happen in a game. But as everything I said, all of the common functions of an upgrade are already covered by other things. I'm just saying that if I'm delivering all that, why would I spend time and resources on something? That's the logic. I think the store on this game is the only one so far that slightly changes its appearance according to the season, and that's an example of something pretty much unneeded like you said, but that adds to the flavor of the game- maybe that, and all the other things mentioned, were the opportunity cost for the developers. Of course there is always room for more, but I guess at some point you just ask "but what for".
Timmy has its own little shop inside the tent, where he sells and buys stuff daily. Then, we need to collect materials and the first shop is built, which offers more things and Tommy begins working there too- this is the first upgrade. Then, we need to wait whatever days and spend whatever money and the shop becomes bigger, offers seasonal stock, etc- this is the second upgrade
tl; dr: Just because previous games did things a certain way, doesn't mean all following games need to follow the same patterns. A company developing something also strives to find the best way to allocate its resources, and I frankly don't see the need of an upgrade just to satisfy old traditions.