Resident Alien is that dreaded Hollywood adaptation of a comic book that most people expect now: a total bastardisation of the original source material. It's a dumbed down, mediocre version of the story that makes the characters behave and talk like dumb TV stereotypes when the original comic consciously avoided doing that at every turn.
Resident Alien was altered for the TV version probably because the producers and writers believed those changes were necessary to get the show greenlit for a series. Live action adaptations of manga are different in Japan. They tend to be at least 80% faithful to the original source material. When there are costumes, the adaptations do their best to create faithful live action versions of the characters' look. Every Japanese live action adaptation of a manga is instantly recognizable from the manga. In Hollywood, the X-Men had to be dressed black leather jumpsuits rather than the rainbow-coloured spandex of the 90s comics. In Japan, could it be that the manga series usually have millions of fans who demand a certain amount of fidelity to the original story? Is it the moral rights of the original authors and creators being respected? Or is fan demand driving the faithfulness? If Resident Alien had been a manga being made into a live action TV show, it would have stuck closely to the original comic with minor changes.
In the US, the comics that get adapted don't often have millions of fans demanding fidelity to the source material unless they're from Marvel or DC, and even those are often changed and fixed in the movie and TV versions. Hollywood generally does not listen to fan demands anyway. In Japan, adapters take the attitude "If it ain't broke, don't fix it." Hollywood adaptations always seek to change to fix things on the way to the screen. It's almost a cliché to expect Hollywood to mess up an adaptation of books and comics, of dumbing down the material. The funny thing is bad adaptations like Resident Alien are now less common than they used to be. At moment, shows like The Boys, Umbrella Academy, The Walking Dead are some of the biggest hits adapted from comics, but they've all been changed from the original comics, but fans and viewers would agree that they improved upon the original material. Maybe that's why a bad adaptation like Resident Alien stood out so much.