Any question that asks “why” can only be answered “because it is your opinion” for any question that asks whether one thing is better or worse than another.
There is no other validation – one thing is not objectively good. They are both the same medium. You favor one.
Manga has a completely different distribution model than comics. Much of the manga has been serialized in publication – or, now, online – allowing it to tell a longer, more complex story, arcs for character development. Comics are marketed as stand-alone items, with fewer and fewer page counts per issue, to reduce costs, so there is less and less room for the story. Check MangaOwl Read Manga Online Free
The manga is created and told by the same team from beginning to end. Comics are worked for different creative teams as the publisher wants. So every 6 or 12 episodes, to shake up sales, they change writers and artists, meaning the previous year’s worth of story was reconnected or rebooted to make way for new ones.
You will never see all the failed manga series. Literally thousands of manga series go and die in one or two chapters, but they are not collected, translated and sold.
Superhero comics sell a superhero, not a story. Characters are sold on their name recognition, not in the ongoing storyline that begins, develops, and ends. Due to the US market approach, Batman sells, not new characters (more,). So if they want to create a new character, companies think they should do it in the context of crossovers or other old character storylines. Having Japanese magazines (and now online versions for test grounds) they can run new ideas and, if that doesn’t work, leave them with little loss.
Manga has an established new-talent recruitment system. Comics are not so.
In Japan, new talents hire competitions, go to events for portfolio review, and develop and sell their entire work in comic markets relatively easily… and now online. Companies pull events for new talent, compete to attract new talent, and look for potential new talent in portfolio reviews. Comics companies have only recently begun to do the last thing, and until then, you are competing with millions of other people to get to know your work. Networking is easy (but still tough) and it’s not impossible to be known for your own work online or in the small press. Once upon a time, you had to get an interview in DC’s NYC office to see. Imagine how many new talents they failed to find that way.
So you like manga better, because you like it. But manga and comics are quite different, as are apples and oranges now, and the only similarity is that they are sequential arts.
Why does manga/anime have much better writing
I hope you don’t actually sit down and read several years’ worth of comics at once, but you sit down and read several years worth of manga at once. In terms of step character development, you see that they are all the same. And the story lines, they are still mined classics.
Where do you think the entire MCU came from? Or X-Men movies, or all Spider-Man movies. Or Deadpool. Superman, Batman, Wonder Woman. Complete CW line-up on TV. Daredevil, Jessica Jones, Luke Cage, Iron First and Punisher on Netflix. Hulu at The Runaways.
The boy of hell. Men in black. Blade. 300. Sin City. Crow. Kick-Ass. Dred. All these were comic books.
Then there are the less anticipated comic books: Road to Pardition. History of violence.
Not to mention Sandman, We for Vendetta, Watchmen, From Hell, Why the Last Man, etc.
And there’s a great manga. Fullmetal Alchemist, Attack on Titan, Black Butler. (I haven’t read the manga as much as I’ve seen anime.)
Comic book and manga art, and art is subjective. I suspect your enmity with Western comic books is your personal taste. And that’s fine.
But don’t blame the media you know little about because it’s not your thing.