Why are so many films nowadays killed by bad writing? (rant)

For a long time I've seen a lot of Hollywood movies that just failed because the writing was just awful, and its a trend that hasn't gone away for a while. Its left me to wonder, why? Do the same bad writers keep getting work to write the same bad movies? Are they just so overworked it'd be impossible for them to write something good? One of the reasons I wanted to become a writer was just so i could try and make less movies that faltered because of this. Especially with big budget animated movies, hours of work and passion are poured into them, but looks can't sell a film, yet that seems like that's what all these company's spend a huge amount of time on.