While a series starring many different creatures for players to catch and keep was a great idea back in the 90s, the Pokemon franchise has ended up running into a problem with how many creatures it has. The series' 8th generation has led to it having a whopping 898 Pocket Monsters. Managing all of those creatures across different titles seemed to become too much for the development team's workload during the development of Sword and Shield, so Game Freak had to make the difficult choice to get rid of the National Dex.