Balatro is, as far as I know, a single person dev team and this is their first game as far as I know.

Hades was made by an established studio that has been around for 17 years and has 25 employees.

Again, a lot of people pick pixel art because they can make all the assets look unified relatively easily. If you've ever come across a game with lots of storebought assets made by different artists you'll know how jarring it is to have wildly inconsistent assets.

They could pick something else, but if it has an extra layer of complexity to getting the assets looking right and unified they may choose not to. You might think "Oh how much art can there be." and the answer for a solo dev is "Oh no too much." especially when they are also designing and programming.

And if you don't care for pixel art there's tons and tons and tons of games without it, so you can go play them instead without it affecting you.

OK but would it have killed Balatro devs use vector graphics like many modern card games on Linux?

Why should they change their art style just for you? This is nothing more than a you problem.