It was a hardware related technical issue that led to a design choice.

Higher fidelity with higher quality animations isn't limited to the battle mechanic. It referred to Pokémon Sword & Shield as a whole meaning every individual characters, buildings, redoing models of past gen Pokémon, developing new Pokémon, routes, towns, etc. on top of the regular game-play which includes battle mechanic, catching mechanic, hold items, abilities, etc. for Sword & Shield.

From what we've seen from the first hand demo footage, more recent footage and full demo play-through alongside comparison videos like Brave Bird comparison [Disclaimer: Third animation showcased in the above video is Giga Impact, not Brave Bird.] and Dragon Pulse, Giga Impact and Water Sport comparison [Disclaimer: Lucario is using Vacuum Wave, not Focus Punch: Ultra Sun & Ultra Moon Vacuum Wave for comparison] every move looks better in Pokémon Sword & Shield in my opinion.

Game Freak improving the game after the first trailer as shown in example A and example B showcases this.