Sora lost most of his powers at the end of DDD so it wouldn't make sense plotwise
Say what you like about Kingdom Hearts, it does a
good job of justifying having to level back up every time. It's not like Metroid where Samus loses all of her stuff every game for no reason (except Fusion. Fusion made sense.) - Chain of Memories starts Sora off with the HP cap from 1, and the rest of his abilities sealed in the cards. 2 has him recovering from a year long memory screw and slumber, 3D is him forcing himself to unlearn his old techniques in favour of formal training, and 3 explicitly explained it.
It amazes me how many RPGs
still mess up this simple facet of immersion. Either let us import our old stats like Quest for Glory (admittedly not a 100% perfect example, the series had an annoying habit of increasing how high your Throwing had to be to throw normal rocks accurately on the field, but given how your inventory capacity was Strength based, you could become superhumanly strong halfway through the series which was nice), Baldur's Gate, or Mass Effect, or explain why we can't, like Kingdom Hearts. (Hell, X-2 was horrible with this, there was no reason why Yuna and Rikku couldn't wreck face from the very beginning with 99999 HP)
And don't get me started on cutscenes that completely mismatch how things work in actual gameplay. Assassin's Creed's Animus sections get a pass on that at least. Not so much the "real" ones.
It was a region locked mission pack and patch that had to be bought standalone even if you owned the original. Talk about a rip off!
Remember when people liked expansion packs? Now you have to download them, they seem to think they're automatically as bad as lootbox microtransactions and live services.