I'm not one of those people super upset about the lack of a National dex; I typically only play through these games a couple times and tend to mostly use new Pokemon anyway. But this isn't a fair summary of things. I've played every mainline Pokemon game to date, but I might not play Sword/Shield. Why? Because their excuse for not having every Pokemon is to improve other aspects of the game, but did that really happen at all? Some of the graphics look like they belong on the N64. Dynamaxing just makes Pokemon really big, unlike mega evolutions which actually changed how the Pokemon looked, and Z-moves which all had unique animations. The models are the same ones they made for X/Y and there are a lot of reused animations, so it's not like including all Pokemon would require remaking hundreds of models and animations from scratch. And these games have been getting easier over the years and haven't even been including challenging post-game content like the Battle Frontier anymore, on top of creating and then scrapping popular mechanics like having Pokemon follow the trainer.
The lack of national dex and the outrage over it is really just all these problems finally coming to an eruption point. After giving and taking so many other things away, they're finally taking away the Pokemon themselves, and people aren't accepting it. Pokemon is the kind of money-printing franchise that absolutely has the ability to make these things happen, so I really can't blame people for calling GF lazy, though I definitely never condone threats and harassment. "Gotta catch some of 'em" doesn't really have a nice ring to it.
This is basically it. I am one of the individuals upset by not having the entire national Dex. Not only does it mean that certain pokemon already getting lost in power creep will fall further behind because they won;t get updates with Gen 8 moves they other wise could have learned or new hold items that could have severly improved how they fight, but also because it is a slippery slope.
They aren't going to select completely "fair" when it comes to choosing each game which pokemon get in. CHarizrad, Lucario, Gardevoir, Pikachu... (and most of Gen 1)With this new policy it's garaunteed that these pokemon will be catchable in every game. On the other end of things, pokemon that they find a far less priority will likely skip two games or even more before they get included, because the risk of not including them is the least.
Sure, most of us won't miss two or three games where Finneion or Swoobat, but for the poor souls who love those pokemon most... They might not even get to see their favorite in HD within the switch's lifespan.
If the leak that has been right about everythig else is right about it's last few predictions, PIkachu is getting a Gigantamax form, Even tho it is catachable early in every game, has the best non legendary Physical electric move (even tho it is a special attack who can make use of better options like thunder bolt) it got two Z moves and a regional evolution.
Charizard is almost certainly getting a gigantamax form (since it is the mascot pokemon of this game's champion) even tho it got 2 Mega evolutions and was a ride pokemon even tho it wasn't native to Alohla.
Meanwhile there are countless pokemon who either were never very useful or who have suffered from severe power creep who have yet to get any real update to their toolkit since their first appearance in their native region. Forgotten and first in line to get skipped over once or twice in future games.
All of that said, the giant mess was made by gamefreak. If they simply said "resources and time were too limited to include everyone" alot of people would have still been made, but they could only be mad at the situation. Instead they felt a need to justify it "We choose quality" time needed for "High quality animations" and most recently "made the models from scratch"
Each one of these claims is either so subjective that there was no point mentioning it, or obviously false (if not false, so poorly implimented for it not to be immediately obvious of new improved work)
These easily countered "reasons" have forced the disenfranchised fans to realize that GF has to either be incompetent (unable to properly manage resources or make new assets that actually look improved) uncaring (making the decision because it best benefits them and trusts the fans will buy it no matter how upset they are) Or lying (trying to placate us with simple falsehoods expecting us to eat it up and understand even tho what they have claimed looks painfully the contrary)
Heck, Japanese fans didn't even get an official announcement of the cut, the majority of Japanese pokemon players didn't find out about it until enough die hards who watched the English Tree House showcase started reporting about it. Even then many Japanese fans requested that GF announce which old pokemon were going to be returning before preorders for the games went live last week in Japanese markets, saying that asking them to preorder a game without the knowledge of which pokemon would be transferable was anti consumer and dishonest.
Whichever one of those three a fan chooses to believe, it's not a good look for GameFreak and the more insincere PR speak or technical excuses they throw, the worse it looks.
's trailer doesn't explain how he survived the Light/Dark rampage, he comes right outta nowhere to help 
