The Real answer for the dexcut is they just fucked up the model and animation importer, and didn't have the manpower with the right knowledge to fix it in time to meet the set release date. So instead they had to put tons of people, including outside help (this is where the ~300 people worked on Sw&Sh number comes from) on (edit recreating here means taking the high quality master versions of the textures and models done in software like Maya, and getting them back into the game engine rendering each and every animation correctly) recreating art assets and getting their busted ass engine to work, since Gamefreak fucking up the importer is actually indicative of their overall software engineering competency.
The original plan months ago was to try to salvage the Sword and Shield launch by not admitting this, as it would be an admission that this was a failed gen, and then having a big surprise announcement of the full dex in the following game/gen with the fixed importer on hand. Their story will be that they listened to feedback and now realize how important the full dex is, while not admitting how incompetent the actual in house Gamefreak devs are to save face; of which less than ~80 of them actually worked on Sword and Shield until recently, many of them off working on Town (btw Town development wasn't going well either, there's just large gaps of software engineering knowledge there) until they realized the importer was totally busted and un-salvageable in time.

Before anyone tells me Masuda said future gens won't have the full dex, he was in those meeting minutes too, right down to that statement being planned as part of how they're going to handle this PR shitstorm.

DEXCUT WAS NOT INTENDED FOR SWORD/SHIELD.