'Pokemon Sword & Shield Won't Let You Transfer Every Old Pokemon Over'
gamespot.com/articles/e3-2019-pokemon-sword-and-shield-wont-let-you-tran/1100-6467720/It's not a temporary thing for this game like in past games, it's a deliberate decision. You'll only be able to transfer a limited number of Pokemon - ones that are already in the game. Mega Evolutions and Z-Moves are also gone, only Dynamaxing is in the game.
During the Treehouse livestream, game producer Junichi Masuda revealed that not every previous Pokemon will be transferable to Sword and Shield. "Players will be able to transfer their Pokemon from Pokemon Home only if they appear in the Galar region Pokedex," Masuda said through an interpreter. What that means is that if a Pokemon isn't already obtainable within Sword and Shield, you won't be able to transfer it over from Pokemon Home.
Masuda acknowledged this is a change from how the previous Pokemon cloud service, Pokemon Bank, worked and explained the rationale behind this controversial decision:
"In previous games that worked with the Pokemon Bank service, you were able to--for example, in Sun and Moon--bring over any Pokemon, even if they weren't in the Alola Pokedex," Masuda said. "But with the transition to the Nintendo Switch hardware, being much more powerful [and] allowing us to be much more expressive with each of the individual Pokemon ... at Game Freak we really spent a lot of time thinking about what the best way to move forward was, really preserving the quality of all the different Pokemon while also taking into account the battle balance, having so many different Pokemon available, all within a limited development time so we don't keep fans waiting too long for every new entry in the series. And after a lot of discussion, we decided to come to a new direction."
Very odd decision from them. They've already reused the same models over and over and they'd even future-proofed them which is why the 3DS games chugged a bit, so it shouldn't have taken that much more work - and they didn't say anything about patching it in... and historically they don't like patching stuff. And they called it a 'new direction' for them implying they haven't done this kind of thing before. We can even see the exact same models being used in Sword and Shield. Also they already implement banlists in tournaments to restrict usage of certain Pokemon which takes care of the balance problem.
And now any Pokemon that gets uploaded to Pokemon Home (released next year as an evolution to Pokemon Bank) will be trapped inside it if they're not in Sword & Shield. >.> Fans of those will have to hope their fave pops up in a newer game I guess. The internet's reception of this news isn't the best, to put it lightly.
Edit: Just adding a couple more things:

Nessa is the Water Gym Leader, who has a Drednaw.

Yamper(Electric) and Impidimp (Dark/Fairy) were also introduced.