I don't know, maybe I'm just not that autistic but this has always been such a non-issue to me.
I don't think I've ever went into a game thinking
>oh since this is a sequel, that means the protagonist is going to have all the powerups I unlocked in the previous game!!
Like, I get it. It's just for gameplay reasons, bro.
If you have an explanation for it, great, if you don't then that's fine too.