Pokémon games have a lot of draws besides cute or cool-looking monsters. They're all about being able to choose your own party, battle, go on an adventure and, most importantly, do so with friends. Even the original game titles had the ability to trade and battle with friends via the Link Cable and later Wi-Fi across generations of games. Sadly, the Nintendo Switch games have lost that. No more can people and friends trade or battle across games if they aren't in the duo usually released. While a lot has been gained feature-wise, this one thing is a step backward which can create a major problem going forward with console mainline games.
There are currently three mainline game Pokémon generations on the Switch: Pokémon Let's Go! Pikachu and Eevee, Pokémon Sword and Shield, and now Pokémon Brilliant Diamond and Shining Pearl. It made sense and was forgivable that Let's Go! was unable to trade with Sword or Shield because it was meant to be simple and is a partner to Pokémon GO. However, BDSP are from a different era and the originals were capable of trading with other generations – so what gives?
One reason may be the rise of Pokémon Home, which makes it a bit of a double-edged sword. Home allows players to move their Pokémon across generations using Pokémon Bank from the 3DS/2DS and even allows Pokémon to be transferred between Let's Go!, Sword and Shield and GO. However, this obviously only applies to that trainer's Pokémon as there's no actual trading, just moving personal Pokémon between games. Not having trading between generations in new games, even remakes, means shoe-horning people into using the Home service -- a paid service -- if they want Pokémon from other games. It takes away from the playing with friends aspect while also forcing the games into their own boxes.
By not being able to trade or battle with others across generations, even online, Nintendo and The Pokémon Company are forcing each title duo into their own corners. It closes off present games from future ones because the majority of players will move onto the next game and those still playing the previous ones become few, making it difficult to trade or battle online and having that aspect die out. The single-player story will always be the central part but without cross-gen, the post-game community will die out faster and make it harder to do other aspects like catching 'em all or competitive battling. If more future games are going to have other online features as well, like Sword and Shield's Max Raid Battles, it makes those features very temporary.
Going forward without having these key features, which until now have been present in every other Pokémon game, is a big mistake. Especially if Nintendo and the Pokémon Company want to move forward with the franchise by having online aspects. There's no reason to not include this feature which has been in every game until the Switch titles besides getting people to use Pokémon Home. It would allow the series to better connect in the future and encourage people to go back to old titles.