Okay, let me drop some numbers.
I'm not sure if this counts the outsourced work, I can't find numbers on those and they're likely lower. Point is, a high schooler working his first job in retail/fast food at minimum wage will make more in a year.
This is the state of animation, as an industry, in Japan. Actually, from what I hear, it's not much better in America. If you wonder why most of our output is "Flash" animated, this is why. It's a dying entertainment industry everywhere, although I'm not sure what it's like in Europe.
So like, really, budget. It's always, always, always, budget. Are there talentless hacks of directors in anime? Yeah, sure. Like there are everywhere. But even the good or genius directors/key-animators are cutting corners like mad, and pouring not only theirs, but their entire team's dedication and energy into maybe a
8-10 second cut out of 20 minutes.
Manga authors make more, but as people have mentioned, it's a static visual medium, and that carries a bucketload of limitations on what it can do, on top of the frantic pace that characterizes work in the manga industry as well.
Also, if you only consume the mainstream stuff that's usually targeted towards kids who expect a certain kind of storytelling, you're going to run into it a lot. Seinen can be better about this, but sometimes even worse because they also tend to be more verbose (verbosity being a "sign" of "maturity"). If you want to be challenged, as with literature or film or any other storytelling form, you need to look outside of the mainstream.
For example,
Ashizuri Aquarium.
(It's magic realism/slice-of-life, and also thinly veiled commentary on the place of children in an increasingly confusing, detached, superficially modernized society. Sounds boring right? Yeah. That's why this stuff never gets made into anime except once in a blue moon.)
If its for kids, then why does it appear in Attack on titan, Death Note, and so many other anime that targets older audiences?
Different cultural standards. Going by American standards, Attack and Titan and Death Note contain too much killing and violence for kids, but that's just business as usual in the world of manga. I don't think they're nearly as prudish as us in this particular area.