You have a game coming up this week.
You haven't had time to prep for the kid. Sudden medical appointments for you, maybe your kid or significent other, and other responsibilities.
You work at least 40 hours a week. You get home tired. Maybe you do essential service and you've been screamed at all day. Maybe you are a salary position and you deal with a lot of overhead work that puts you over 40 hours a week.
So you're tired. You got chores to do. You have to eat. You have to cook. You have to clean. Now, you just want to decompress.
Instead of watching something with your family, or reading, or scrolling through social media, you decide to pick up your favorite 5E D&D rulebook. You want to run D&D again with your friends or your family. They want something that is a little harder then before, so you want to think maybe T2 for your adventure. One-shots are all you really have time for, but they really want a good story. Let's say you want to prep for 3 sessions.
Now to construct the game. Again you're tired. There's literally a million other things you could be doing right now to have fun, decompress, and relax. But you choose this one.
...Until you open the book. You read, I don't know, a Necromancer's stat line. You want to do some dark magic stuff. But all these spells...and it can only cast one per turn. So now you have to parse, let's say, 5 spell levels worth of effects, and then decide which spells to cast at which level, and which spells were already cast, and what spells will be the most fun. You're not able to DM too much, or read the books too much, so reading all the spells takes maybe an hour or two to really understand what's going on.
Oh...now its 9. Kid has to go to bed. Or now its 10, and I have to be up at 5am. You didn't even get to really prep the game, and you don't feel too equipped to want to run it as is.
So the next day comes, but you aren't able to prep because life gets in the way. Then the next day. The session is tomorrow, and you've forgotten what all these spells do for the most part because of work or other responsibilities. Eh...maybe you don't need this necromancer. Maybe just some fighting character that can cast a couple of spells 2/day or 1/day.
This is why we have the new stat blocks.
If you do not respect the people who play the game and don't have the time to master it like you do, then no, WotC is not obligated to care about your opinion or what you want. People have been asking for an easier D&D to play that still has some meat, and this is WotC creating that.
All these arguments about how easy it is to write down spells and so on are not good arguments. Not a single one of them is. The time concerns you have throughout the day, and the time concerns I or others have throughout the day, are not the same. Me and others are not obligated for any reasons to adhere to your standards of play, and we don't want to have to stress over huge spell lists anymore. Given us tight spell lists and spell like abilities.
Yes, WotC should put an expanded spell list in the flavor text of the monster. Vecna should have 3 spell list that you can choose from to use if you want to put in more time to prep the game. But the base of the game ought to be easy to pilot. The base of the game ought to be simple to understand.
Stop holding others to your standards. Accept that D&D is for everyone. Its ok to to ask for more, but stop asking for more at the expense of others. Have some respect for your fellow gamers.
How is that too much to ask for?